• Preheat oven to 350 degrees. Lightly spray an 8 x 8" square pan or baking dish with non-stick baking spray. Set aside.
• To a mixing bowl add the sour cream, sugar, egg, oil and vanilla. Whisk together well until smooth. Set aside.
• In a separate bowl, combine the dry ingredients; 1 1/2 cups flour, baking powder and salt. Whisk together well. Gradually add the dry ingredients to the wet ingredients. Using a large whisk, combine well. The batter should be thick, smooth and lump-free.
• In a small bowl, add the blueberries and remaining 1 tablespoon of flour. Coat the blueberries in the flour. (If using frozen blueberries, make sure they are thawed completely.) Add the coated blueberries to the cake batter. Using a rubber scraper gently fold the blueberries into the batter.
• Pour the batter into the prepared pan, spreading the batter evenly into the bottom of the pan.

Crumb Topping:

• In a separate bowl, combine the flour, brown sugar and cinnamon (if using) with a fork. Add in the melted butter and combine to create a crumble, gravel-like texture. Sprinkle the crumble topping over the top of the coffee cake batter.
• Bake the coffee cake at 350 degrees for 40-45 minutes. The center of the cake should be set and firm. To test for doneness, insert a toothpick into the center of the cake. If the toothpick comes out clean and crumb-free the cake is done.
• Remove from oven and let cool for 10-15 minutes. Mix together the glaze, by combining the powdered sugar and milk in a small bowl. Mixture will be slightly thick. Drizzle over the top of cake. Let glaze set for 10 minutes before slicing and serving.