Streusel:
1/2 cup chopped nuts
1/3 cup firmly packed brown sugar
1/4 cup granulated sugar
2 tablespoons (1/4 stick) butter, cut into small pieces
1 teaspoon cinnamon

Cake:
1/2 cup (1 stick) butter, room temperature
1 cup granulated sugar
1/4 cup Basic Sourdough Starter
2 eggs
1 teaspoon vanilla extract
2 cups all-purpose flour
1 teaspoon baking soda
1 teaspoon baking powder
1/2 teaspoon salt
1 cup sour cream
Confectioner's sugar

 For streusel: Combine all ingredients in small bowl and set aside.
For cake: Preheat oven to 350 degrees F. Grease a 9- or 10-inch Bundt pan. Cream butter with granulated sugar in large bowl. Add starter, eggs and vanilla and beat until smooth. Sift dry ingredients and add alternately to creamed mixture with sour cream, beating well after each addition. Pour half of batter into pan and sprinkle with half of streusel mixture. Cover with remaining batter and top with remaining streusel. Bake until tester inserted in center of cake comes out clean, about 45 minutes. Remove cake from pan and let cool on wire rack. Sprinkle with confectioner's sugar before serving.