Preheat your oven to 350°F (175°C). Grease a 9-inch round or a 8-inch square pan with butter or cooking spray. Use a round springform or line the square pan with parchment with the edges overhanging if you want to remove the cake from the pan after cooling. Set aside.

Make the streusel: In a small bowl, combine the flour, brown sugar, and ground cinnamon until well blended and there are no lumps. Use a fork, pastry cutter or clean fingers to cut the cold cubed butter into the dry ingredients until crumbly. Place in the fridge while until needed.

Mix the batter: In a medium bowl, whisk together the flour, baking powder, baking soda, and salt. Set aside. In a large mixing bowl, cream together the softened butter and sugar until light and fluffy. Beat in the eggs and vanilla extract. Finally, beat in the sour cream. Add the dry flour mixture to the creamed mixture; mix until just combined. Gently fold in 1 cup of the blueberries.

Assemble the coffee cake: Spread the cake batter into the prepared baking pan. Sprinkle the streusel topping evenly over the batter. Top with the remaining blueberries.

Cool and serve: Once baked, remove the coffee cake from the oven and let it cool in the pan for about 15 minutes. Serve the cake straight from the pan or remove it to a platter (if you used parchment). Serve it warm or at room temperature.