• Preheat the oven to 350 degrees. Spray a 9 by 13 inch baking dish generously with cooking spray. Set aside.

To Make Streusel Topping

• In a small bowl, whisk together the dry ingredients for the streusel topping - 1 cup packed brown sugar, and all purpose flour.
• Using a pastry cutter or a fork, cut the butter into the dry ingredients until the mixture is crumbly. Set aside.

For the Cake Batter

• In a large bowl whisk together the flour, baking powder, baking soda, and salt. Set aside.
• In a stand mixer fit with the paddle attachment or in a large bowl using a hand mixer, beat the butter and granulated sugar together until light and fluffy, about 3 to 6 minutes.
• Add in the eggs, one at a time. Now beat in the lemon juice and vanilla extract. Scrape down the sides, and beat in the sour cream and lemon zest until the mixture is smooth and combined. Scrape down the sides again.
• Add in the flour mixture, beat on a low for a few moments until you are able to beat on high until the mixture is just combined. The batter will be thick and sticky. Stir in the blueberries.
• Pour the batter into the prepared pan. Add the topping and bake for 40 to 45 minutes or until a toothpick inserted int the middle comes out with just a few crumbs.

For Icing

• Before serving, whisk together the powdered sugar and milk. If necessary, add a little more milk until the mixture is runny. Drizzle over the coffee cake.