Prepare the Streusel: In a medium bowl, combine flour, brown sugar, cinnamon, and cold unsalted butter. Mix until mixture resembles coarse crumbs, then set aside.

Mix Dry Ingredients: In a separate large bowl, whisk together all-purpose flour, baking powder, baking soda, and salt. Set aside.

Cream Butter and Sugars: Beat the softened unsalted butter with granulated sugar and brown sugar in a stand mixer until light and fluffy, about 3-5 minutes.

Incorporate Wet Ingredients: Add sour cream, eggs, and vanilla extract to the creamed mixture, mixing until smooth, about 2 minutes.

Combine Mixtures: Gradually add dry ingredients to wet mixture, mixing slowly until just combined.

Add Blueberries: Gently fold in the blueberries with a spatula, distributing them evenly.

Bake: Pour batter into a greased 9x13 inch baking pan and sprinkle streusel on top. Bake at 350°F (175°C) for 50 minutes.

Make the Glaze: Whisk together powdered sugar and softened cream cheese until smooth. Drizzle over the cooled cake.