Chocolate cookie wafers:
1/4 cup plus 2 tablespoons cake flour (not self-rising)
3 tablespoons plus 2 teaspoons unsweetened, non-alkalized cocoa powder
1/2 teaspoon black pepper
3 large egg whites, at room temperature
3/4 cup plus 2 tablespoons confectioners' sugar, sifted
3 tablespoons unsalted butter, melted
3/4 teaspoon vanilla extract

Chocolate mousse:
7 ounces semisweet chocolate, coarsely chopped
1/3 cup milk
2 tablespoons granulated sugar
Pinch of salt
2 tablespoons vegetable oil
1 tablespoon port
1 tablespoon vanilla extract
1 cup heavy cream

Port aspic:
1 1/4 cup water, divided
1 envelope unflavored powdered gelatin
1 cup port
2 tablespoons granulated sugar

Garnish:
Confectioners' sugar
Cocoa powder

Make the chocolate cookie wafers:
Position a rack in the lower third of the oven and preheat to 275 degrees F. Generously butter two large baking sheets. Cut a 3 1/2 inch circle out from a plastic coffee can or similar lid. Discard the center. The outer rim of the lid will be used as a stencil for the wafers.
Into a large stainless steel bowl, sift together the flour, the cocoa, and the black pepper.
In a 4 1/2-quart bowl of a heavy-duty electric mixer fitted with the wire whip attachment, on medium speed, beat the confectioners' sugar and the egg whites until well combined. Continue beating on medium-high speed until glossy and stiff peaks form, about 5 to 6 minutes.
With a large rubber spatula, fold 1/3 of the flour mixture into the stiff egg white/sugar mixture. Fold in the vanilla and half of the melted butter. Fold in another third of the flour mixture. Fold in the rest of the melted butter and the flour mixture.
Place the prepared wafer stencil on the baking sheet. Fill the stencil with a very thin layer of the wafer batter, smoothing it evenly with a small metal spatula. Repeat this process with the remaining batter. Bake the wafers for 12 to 15 minutes, until firm and no longer sticky. The wafers should still be pliable when they come out of the oven, but will become crisp as they cool. Carefully remove the individual wafers to a cooling rack to finish cooling.

Make the chocolate mousse:
Place the chocolate in a food processor fitted with the metal chopping blade. Process for 20 to 30 seconds, until finely ground.
In a small saucepan, combine the milk, sugar and salt. Cook over medium heat, stirring with a wooden spoon, until the sugar dissolves and the milk comes to a boil. Remove the pan from the heat.
With the motor of the food processor running, pour the hot milk through the feed tube. Process for 10 to 20 seconds until the chocolate is completely melted. Using a spatula, scrape down the side of the work bowl. Add the oil, port, and vanilla; process for 5 to 10 seconds, until the mixture is creamy. Scrape the chocolate mixture into a large bowl and cool for about 5 minutes, until tepid.
In a 4 1/2-quart bowl of a heavy-duty electric mixer using the wire whip attachment, whip the cream until soft mounds barely start to form and the cream is still pourable. Do not overwhip the cream.
Using a rubber spatula, gently fold one third of the whipped cream into the tepid chocolate mixture to lighten it. Fold in the remaining whipped cream. Do not overfold the mousse or the texture will be grainy. Refrigerate until ready
to serve.

Make the port aspic:
Measure 1/4 cup of water into a medium-sized heatproof ramekin. Sprinkle the gelatin over the water and let the mixture soften for five minutes.
In a medium saucepan, set over medium heat, bring the port, 1 cup of the water and the sugar to a boil. Remove the pan from the heat.
Immediately scrape the gelatin mixture into the hot port/sugar mixture and stir to combine. Stir occasionally while the mixture cools, for about 15 minutes.
Pour a thin layer of the port aspic over each of 8 dessert plates. Chill until set.

Choose the eight prettiest cookie wafers and reserve them for the tops of the desserts. If desired, dust with confectioners' sugar and cocoa powder.
To serve, arrange one chocolate wafer in the center of each dessert plate. Fill a pastry bag fitted with a large star tip (such as Ateco #5) with the chocolate mousse. Pipe a layer of chocolate mousse over each wafer. Place another cookie on top of the mousse, and pipe another mousse layer. Finish with the reserved chocolate wafers.

 
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