UPDATE 5/23/2011: I made this cake again and tried to make it more healthy. I successfully substituted half the flour with white whole wheat flour and only sprinkled one tablespoon of turbinado sugar on top instead of two. Both adjustments went unnoticed, which means success!
Blackberry Rhubarb Buttermilk Cake
1 cup all-purpose flour
1/2 teaspoon baking powder
1/2 teaspoon baking soda
1/4 teaspoon salt
1/2 stick unsalted butter, softened
2/3 cup sugar
1/2 teaspoon pure vanilla extract
1 large egg
1 teaspoon lemon zest
1/2 cup well-shaken buttermilk
3/4 cup fresh blackberries
1/2 cup rhubarb, chopped
2 tablespoons turbinado sugar
1. Preheat oven to 400°F with rack in middle. Coat a 9-inch round cake pan with cooking spray.
2. Whisk together flour, baking powder, baking soda, and salt in a small bowl. Set aside.
3. Beat butter and 2/3 cup sugar with an electric mixer at medium-high speed until batter is smooth, about 2 minutes. Beat in the vanilla, egg, and lemon zest. Mix until well combined.
4. At low speed, mix in the flour mixture in 3 batches, alternating with buttermilk. Start with the flour and end with the flour. Mix until just combined. Don’t over mix.
5. Spoon batter into cake pan, smoothing the top with a spatula. Scatter blackberries and rhubarb evenly over the top of the batter. Sprinkle with remaining 2 tablespoons of turbinado sugar.
6. Bake until cake is golden brown and a wooden pick inserted into center comes out clean, 20-25 minutes. Let the cake cool in pan for about 10 minutes, then turn out onto a rack and cool completely. Serve the cake upside down to show off the pretty berries and rhubarb. Cut into slices.