This is a great recipe from Lou Seibert Pappas.
Blueberry Streusel Coffee Cake
Yield: 1 9-inch cake; serves 10
½ cup canola oil
½ cup firmly packed light brown sugar
½ cup granulated sugar
2 large eggs
1-teaspoon vanilla extract
1 cup unbleached all-purpose flour
1-cup whole-wheat flour
1-teaspoon baking powder
1-teaspoon baking soda
¼ teaspoon salt
1-cup buttermilk or low-fat plain yogurt
2 cups fresh or frozen blueberries or mixed blackberries, blueberries, and raspberries
2 tablespoons cold unsalted butter, cut into bits
¼ cup unbleached all-purpose flour
1/3 cup firmly packed light brown sugar
2 teaspoons ground cinnamon
1 cup (4 ounces) walnuts, chopped
Preheat the oven to 350˚F. Lightly butter and flour a 9-inch springform pan.
To make the streusel topping: In a medium bowl of a food processor, combine the butter, flour, brown sugar, and cinnamon. Cut the butter in with your fingers or process until the mixture forms coarse crumbs. Stir in the nuts and set aside.
In a large bowl, combine the oil, sugars, eggs, and vanilla and beat with a wooden spoon or electric mixer until smooth. In a medium bowl, combine the flours, baking powder, baking soda, and salt. Stir in the berries. Turn into the prepared pan and sprinkle evenly with the topping.
Bake for 35 to 40 minutes, or until the cake is golden brown and a cake tester inserted in the center comes out clean. Let cool in the pan on a wire rack for 10 minutes, then remove the pan sides and let cool completely. Cut into wedges to serve.