Preheat oven to 350°F. Prepare a 9-inch cake pan with parchment paper and grease the sides.

In a medium bowl, combine flour, brown sugar, cinnamon, melted butter, and salt to make the streusel topping. Mix until crumbly and set aside.

In another bowl, whisk together all-purpose flour, baking powder, and salt for the batter.

In a large bowl, beat together sugar and butter until light and fluffy. Add sour cream, milk, egg, and vanilla extract; mix until combined.

Gradually add dry ingredients to wet ingredients and mix until just combined.

Spread half of the batter into the prepared pan. Sprinkle with half of the blueberries and half of the streusel topping.

Repeat with remaining batter, blueberries, and streusel topping.

Bake for 32-38 minutes or until a toothpick inserted in the center comes out clean. Allow to cool before serving.

To prepare the glaze, whisk powdered sugar, milk, and vanilla extract until smooth. Drizzle over cooled cake.