Blueberry Crumb Cake

From Martha Stewart

Tossing the blueberries with a bit of flour keeps them from sinking during baking. When making streusel, squeeze the mixture into large crumbs so it forms a crisp topping as it bakes instead of melting into the batter.

Serves 9

Ingredients
For the Streusel Topping
        1 cup all-purpose flour
        1/2 cup packed light-brown sugar
        1/4 teaspoon salt
        1/2 cup (1 stick) cold unsalted butter
   
For the Cake
        4 tblspn unsalted butter, softened, plus more for pan
        1 1/2 cups all-purpose flour, plus more for pan
        1 1/2 teaspoons baking powder
        1/2 teaspoon baking soda
        1/4 teaspoon salt
        1/4 teaspoon allspice
        3/4 cup granulated sugar
        1 large egg
        2/3 cup low-fat buttermilk, well shaken
        1 1/2 cups blueberries
        Confectioners' sugar, for dusting

Method
Preheat oven to 350°F. Make streusel topping: In a medium bowl, stir together flour, brown sugar, and salt. Cut in the butter using your hands or a pastry blender until large, moist crumbs form. Chill.

Butter and flour a 9-inch square baking pan. In a medium bowl, whisk together 1 1/2 cups flour, baking powder, baking soda, salt, and allspice. In a large bowl, beat the butter and granulated sugar with an electric mixer until fluffy. Add egg; beat well. Add flour mixture and buttermilk alternately until just combined. (Batter will be very stiff.) In a large bowl, toss the blueberries with remaining teaspoon flour. Fold blueberries into the batter; spoon into prepared pan.
   
Sprinkle cake with streusel topping. Bake until golden brown and a tester comes out clean, 45 to 50 minutes. Let cool completely. Dust with confectioners' sugar before cutting into squares.