Cocoa sponge cake:
1/3 cup sifted cake flour (not self-rising)
1/4 cup sifted unsweetened alkalized cocoa powder
1/3 cup plus 2 tablespoons granulated sugar, used in
three separate measurements
1/4 teaspoon double acting baking powder
1/8 teaspoon salt
2 large eggs plus 2 large egg yolks,
separated (at room temperature)
3 tablespoons vegetable oil
2 teaspoons water
1 teaspoon vanilla extract

Orange syrup:
1 navel orange
2 tablespoons granulated sugar
3 tablespoons Grand Marnier

Dark chocolate mousse:
8 ounces semisweet chocolate, coarsely chopped
1/2 cup milk
1 tablespoon vegetable oil
4 teaspoons vanilla extract
3/4 cup heavy (whipping) cream

White chocolate orange mousse:
3 tablespoons Grand Marnier
1 1/4 teaspoons unflavored powdered gelatin
6 ounces white chocolate, finely chopped
1/4 cup milk
1 3/4 teaspoons minced orange zest
(reserved from orange syrup)
1 tablespoon vegetable oil
2 teaspoons vanilla extract
1 cup heavy (whipping) cream

Chocolate glaze:
6 ounces semisweet chocolate, finely chopped
2/3 cup heavy (whipping) cream
2 tablespoons light corn syrup
1 teaspoon vanilla extract
Orange slices, for garnish

Make the cocoa sponge cake:
1. Position a rack in the center of the oven and preheat to 350 degrees F. Line a 15 1/2-by-10 1/2-by-1-inch jellyroll pan with aluminum foil, leaving a 2-inch overhang on the short ends. Fold the overhang underneath the pan. Butter the aluminum foil and the sides of the pan. Lightly dust the bottom of the pan with flour and tap out the excess.
2. In a small bowl, using a wire whisk, stir together the flour, cocoa, 2 teaspoons of the sugar, baking powder and salt, until thoroughly blended. Sift the flour mixture onto a piece of waxed paper.
3. In a 4 1/2-quart bowl of a heavy-duty electric mixer, using the wire whip attachment, beat the egg yolks at medium-high speed. Add 1/3 cup of the remaining sugar in a steady stream. Continue beating the egg yolks for 4 to 7 minutes, until the batter is pale yellow and forms a thick ribbon. Lower the speed to medium and beat in the oil, water and vanilla.
4. In a grease-free 4 1/2-quart bowl of a heavy-duty electric mixer, using a clean wire whip attachment, beat the egg whites at low speed until frothy. Gradually increase the speed to medium-high and continue beating the whites until they start to form soft peaks. One teaspoon at a time, gradually add the remaining 4 teaspoons of sugar and continue to beat the whites until they
form stiff, shiny peaks.
5. Scrape one-third of the whites on top of the beaten egg yolks. Resift one-third of the flour mixture over the whites and using a balloon whisk or a large rubber spatula, fold the flour mixture and egg whites into the egg yolk mixture making sure to bring the whisk or spatula near the bottom of the bowl to free any flour that may be clinging to the side of the bowl. One-third at a time, gently fold in the remaining whites with one-third of the resifted flour mixture. Do not overfold the batter. Scrape the batter into the prepared pan and spread it into a thin, even layer with an offset metal cake spatula.
6. Bake the sponge cake for 10 to 15 minutes, until the center springs back when gently pressed with a finger. Transfer the pan with the sponge cake to a wire rack to cool for 10 minutes. Using the foil as handles, lift the cake from the pan and set it on a wire rack to cool completely.

Make the orange syrup:
7. Using a swivel vegetable peeler, peel off eight 3/4-by-2 1/2-inch strips of orange zest. Be careful to not include any of the bitter white pith beneath
the orange skin. With a large, sharp knife, mince the zest to make 1 3/4 teaspoons. Set the zest aside to be used when making the white chocolate orange mousse. Squeeze the juice from the orange to make 1/4 cup.
8. In a small saucepan, combine the orange juice and sugar. Cook over medium heat, stirring constantly with a wooden spoon until the sugar
dissolves completely and the mixture is hot. Do not let the syrup boil.
Remove the pan from the heat. Stir in the Grand Marnier and cool the
orange syrup to room temperature.

Make the dark chocolate mousse:
9. Put the chocolate in a food processor fitted with the metal chopping
blade. Process for 30 to 45 seconds, until finely chopped.
10. In a small saucepan, set over medium heat, bring the milk to a gentle
boil. With the motor of the food processor running, pour the hot milk
through the feed tube. Process for 15 to 25 seconds, until the chocolate
is completely melted. Scrape down the side of the workbowl. Add the
oil and vanilla to the chocolate mixture. Process for 15 to 25 seconds,
until the mixture is smooth and creamy. Scrape the chocolate mixture
into a large bowl. Let the chocolate mixture stand for a few minutes,
until tepid.
11. In a chilled 4 1/2-quart bowl of a heavyduty electric mixer, using the
wire whip attachment, whip the cream at medium-high speed, until soft mounds barely start to form and the cream is still pourable. Do not
overwhip the cream.
12. Using a large rubber spatula, gently fold one-third of the whipped
cream into the tepid chocolate mixture to lighten it. Fold in the remain-
ing whipped cream. Do not overfold the mousse or it will become
grainy. Cover the surface of the mousse with plastic wrap and freeze
for about 30 minutes, until it starts to set.

Line the loaf pan with sponge cake:
13. Cover the cooled sponge cake with a flat baking sheet and invert the
cake. Carefully peel off the aluminum foil. Cover the sponge cake with
a piece of waxed paper and top with a flat baking sheet. Reinvert the
sponge cake so that it is right side up.
14. Using the bottom of 9 1/4-by-5 1/4-by-2 3/4-inch non-stick metal loaf
pan (such as Ekco Baker's Secret) as a guide, cut a rectangular piece of
sponge cake big enough to cover the bottom of the loaf pan. In the same manner, cut two pieces of sponge cake to line the two long sides of the
loaf pan. Cover the remaining piece of sponge cake with plastic wrap
and reserve to later top the mousse-filled mold. The two short ends of
the loaf pan will not be lined with cake.
15. Line the bottom and sides of the loaf pan with a double thickness of plastic wrap so that the plastic extends about 1 inch beyond the rim
of the pan.
16. Brush the tops of the three cut pieces of sponge cake with three-
quarters of the orange syrup. Line the bottom and one long side of
the loaf pan with two pieces of the sponge cake. Cover the pan
and the remaining cut piece of sponge cake with plastic wrap and
set aside while preparing the white chocolate orange mousse.

Make the white chocolate orange mousse:
17. Put the Grand Marnier in a small heatproof cup. Sprinkle the gelatin
over the liqueur and let the mixture soften for 5 minutes.
18. Place the cup with the softened gelatin in a saucepan with enough
water to come halfway up the side of the cup. Heat the gelatin mix-
ture in hot, not simmering water. Stir the gelatin mixture frequently
for 2 to 3 minutes, until the gelatin granules dissolve completely and
the mixture is clear. Remove the pan from the heat. Leave the cup
containing the gelatin mixture in the hot water to keep the gelatin hot
until ready to use.
19. Put the white chocolate in a medium bowl. In a small saucepan, heat
the milk with the reserved 1 3/4 teaspoons orange zest over medium
heat until the milk comes to a boil. Pour the hot milk mixture over the
bowl of chocolate. Let the mixture stand without stirring. Pour the hot
gelatin over the chocolate/milk mixture. Gently whisk until smooth. Stir
in the oil and vanilla until blended. Let the mixture cool for 10 to 15
minutes, until tepid.
20. In a chilled large bowl, using a handheld electric mixer, set at medium-
high speed, whip the cream just until soft mounds barely start to form
and the cream is still pourable. Do not overwhip.
21. Using a rubber spatula, temper the tepid white chocolate mixture/
gelatin mixture by folding one-fourth of the whipped cream into
it just until blended. Fold in the remaining whipped cream. Do
not overfold or the mousse will become grainy. Leave the white
chocolate orange mousse at room temperature.

Fill the loaf pan:
22. Remove the dark chocolate mousse from the freezer. Position the loaf
pan so that the one long side that is lined with sponge cake is lying
parallel in front of you. Slightly tilt the front of the pan towards you
by propping up the back of the pan lengthwise with the long handle
of a wooden spoon.
23. Scrape the chocolate mousse into the loaf pan and using a small offset metal cake spatula, carefully spread the mousse so that it covers the
piece of sponge cake on the bottom of the pan and fills in the cake-
lined space between the far edge of the bottom of the pan and the
opposite rim at the top of the pan. The dark chocolate mousse will
fill half of the loaf pan on the diagonal forming a wedge shape. (At
serving time, when the cake is cut crosswise, the dark and white
chocolate mousses will form two opposed triangles.)
24. Cover the unlined long side of the pan with the third cut piece of moistened sponge cake. Carefully fill the empty wedge-shaped space
with the white chocolate orange mousse. Trim the remaining piece of
sponge cake to fit the top of the mousse-filled loaf pan. Brush the
trimmed piece of sponge cake with the remaining orange syrup. Cover
the loaf pan with the moistened side of the sponge cake lying against
the mousse. Wrap the loaf pan in plastic and aluminum foil. Freeze
the mousse cake for at least 6 hours or overnight, until firm. If
desired, the mousse cake may be kept frozen for up to 1 month.

Unmold the mousse cake:
25. Cover a 9 1/2-by-5-inch cardboard rectangle with aluminum foil.
Unwrap the mousse cake and put the foil-covered rectangle on top
of the cake. Invert the loaf pan onto the cardboard rectangle. Gently
pull down on the ends of the plastic wrap until the cake releases from
the sides of the pan and onto the cardboard rectangle. Put the card-
board rectangle with the mousse cake onto a wire rack set on a baking
sheet. Refrigerate the mousse cake while preparing the chocolate glaze.

Make the chocolate glaze:
26. Put the chocolate in a medium bowl. In a small saucepan, set over medium heat, heat the cream and corn syrup until the mixture comes
to a boil. Pour the hot cream over the chocolate. Let the mixture stand
for 30 seconds to melt the chocolate. Gently whisk until smooth. Stir
in the vanilla.
27. Remove the plastic wrap from the chilled mousse cake. Spoon the
warm chocolate glaze over the mousse cake, coating it completely.
Transfer the mousse cake still on the cardboard rectangle to a clean
baking sheet. Put the baking sheet with the glazed mousse cake in the
freezer until ready to serve. (The mousse cake is easier to cut when
kept frozen.)
28. With a sharp, thin-bladed knife, cut the mousse cake into 10 pieces, wiping the knife blade clean between each slice. Lay the slices on
dessert plates. If desired, garnish the plates with orange slices cut
into small triangles. Let the mousse cake soften at room tempera-
ture for 5 to 10 minutes before serving.

 
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