From Whole Grain Baking, King Arthur Flour
Yield: Two 9-inch round cakes or one 9 x 13-inch cake, serves 24
2 cups whole wheat pastry flour
1/2 cup unbleached all-purpose flour
1 teaspoon baking soda
1 teaspoon salt
1/2 cup (1 stick) unsalted butter, at room temperature
1 cup sugar
1 large egg
1 cup buttermilk*
1 1/2 teaspoons vanilla extract
2 cups peeled, diced fresh peaches
2 tablespoons unsalted butter, at room temperature
1/2 cup sugar
1 tablespoon unbleached all-purpose flour
1 tablespoon ground cinnamon
1. Preheat the oven to 350 degrees F. Grease and flour two 9-inch round pans or one 9 x 13-inch pan.
2. Make the cake batter: Whisk together the dry ingredients (pastry flour through salt) and set aside. Cream together the butter and sugar in a large bowl. Beat in the eggs, stopping to scrape down the sides of the bowl. Add the dry ingredients, one third at a time, alternating with the buttermilk. Add the vanilla. Fold in the peaches until evenly distributed. Pour the batter into the prepared pans and smooth down with a rubber or offset spatula.
3. Make the topping: Combine all the topping ingredients in a small mixing bowl and combine until it looks like wet sand (I found that using my hands was the easiest way to do this). Sprinkle mixture evenly over the batter.
4. Bake according to pan size–25-30 minutes for the two rounds, 30-35 for the one rectangle–until the top is golden brown and a cake tester or toothpick inserted into the center comes out clean. Remove from the oven and cool on a rack for at least 20 minutes before serving.
*I didn’t have any buttermilk around, so I made my trusty substitute: 3/4 cup plain whole milk yogurt + 1/4 cup water for every cup of buttermilk. If you look online you can find other options, namely souring some milk with lemon juice or vinegar, but I prefer the texture that results from the yogurt plus water.