Preheat oven to 350°F and line an 8x8 square cake pan with parchment paper, or coat lightly with nonstick spray.
In a large bowl, combine flour, granulated sugar, baking powder, salt, and cinnamon.
Whisk together milk, egg, and vanilla, then pour into dry ingredients and stir to combine.
Fold in blueberries, then pour batter into prepared pan.
To make the streusel, in a small bowl combine flour, brown sugar, granulated sugar, and salt. Cut in butter using a fork until mixture forms large crumbs. Scatter over the top of the batter.
Bake for 30-35 minutes or until golden brown and a toothpick inserted into the center comes out clean.