A tender, buttery crumb cake filled with wild blueberries and topped with a sweet cinnamon streusel. Perfect for breakfast, brunch, or dessert with coffee or ice cream.
Prep the oven and pan. Position a rack in the center of the oven and preheat it to 375°F. Grease and flour a 9-inch square baking pan.
Make the batter. Mix the butter, sugar, and eggs. Beat the butter and sugar together with an electric mixer until light and fluffy, or about 3 minutes. Add the egg and vanilla and beat until blended.• Combine the flour, baking powder, and salt in a bowl and stir to blend. Add approximately one-third of the dry mixture to the first mixture, using half of the milk. Beat until smooth. Repeat this process with the remaining 1/3 of the dry mixture and the remaining milk. Add the last of the flour mixture and beat just until smooth.• Fold the blueberries into the batter.
Spread the batter in the pan. Spoon the batter into the prepared baking pan and spread gently.
Make the topping. Combine 4 tablespoons of unsalted butter with the brown sugar, 1/3 cup of flour, and cinnamon; blend with a fork or your fingers to make the crumb topping. Sprinkle the topping mixture over the cake batter.
Bake the cake. Transfer the cake to the oven and bake for 25 to 35 minutes or until it springs back when lightly touched. A toothpick should come out clean when inserted into the center of the cake.
Serve. Slice the cooled cake and serve on small plates with extra berries or a scoop of ice cream.