• Heat oven to 375°F. Then prepare a 8"x8" or 9"x9" baking dish by greasing it with butter and dusting it with flour.

Prepare the Streusel Topping

• In a mixing bowl, add the sugar, flour, cinnamon, and butter. Use a pastry cutter to cut the butter into the dry ingredients until the mixture is crumbly and the size of peas.

Make the Cake Batter

• In a mixing bowl, cream together the butter and sugar, using a mixer.
• Mix in the egg and vanilla extract.
• In a separate mixing bowl, add the flours, baking powder, baking soda, and salt. Stir together.
• Add the dry ingredients to the creamed mixture alternately with the buttermilk.
• Fold the blueberries into the batter gently.
• Spread the thick batter in the prepared baking dish in an even layer.
• Spread the topping over the batter evenly.
• Bake for 50 minutes, or until the center is done and the topping is a light golden brown.