Combining blackberries with blackberry preserves for the topping brings out the best in the berries.
2 cups cake flour (not self-rising)
1 teaspoon baking powder
1 teaspoon baking soda
3/4 teaspoon salt
1/2 cup unsalted butter, softened
1 cup sugar
1 teaspoon vanilla
2 large eggs
1 cup buttermilk (shake well)
3/4 cup sweet white dessert wine
4 tablespoons sugar
1 (3- by 1-inch) strip fresh orange zest
1/2 cup blackberry preserves without seeds
4 cups fresh blackberries (1 1/2 lb)
Preheat oven to 350. Line the bottom of a buttered 9- by 2-inch round cake pan with a round of wax paper, then butter paper. In a bowl sift together the flour, baking powder and soda, and salt and set it aside. In the bowl of an electric mixer combine the butter and sugar and beat until pale and fluffy, then beat in vanilla. Add the eggs 1 at a time, beating well after each addition, then, with mixer at low speed, beat in all of the buttermilk until just combined. Add flour mixture in 3 batches, mixing after each addition until just combined. Spoon batter into cake pan, smoothing top, and bake in middle of oven until golden and a tester comes out clean, 40 to 50 minutes. Cool in pan on a rack 10 minutes, and then run a thin sharp knife around edge of cake to loosen. Invert onto rack, and then slide cake onto a cake plate.
Make topping: In a saucepan combine the wine, 3 tablespoons sugar, and
zest and bring the mixture to a boil, stirring until sugar is dissolved. Boil until the syrup is reduced to about 2/3 cup, 1 to 2 minutes. Discard zest. Reserve 2 tablespoons syrup and pour remainder slowly and evenly over cake (cake will absorb syrup). Stir together reserved syrup, preserves, and remaining tablespoon sugar in small saucepan and simmer, stirring occasionally, until thickened slightly, about 1 minute (it should be the consistency of a thick syrup). Put blackberries in a large bowl, then pour the preserves mixture over berries. Gently stir berries with a rubber spatula to coat, then pour over cake, mounding blackberries on top. Serve warm or at room temperature. Cake can be made (without syrup and topping) 1 day ahead, cooled completely, then kept at room temperature, wrapped in plastic wrap. Serves 8.