Preheat the oven to 350ºF.
Prepare a 9-inch round springform pan with non-stick spray and set aside.
To prepare the streusel, add flour, brown sugar, cinnamon and melted butter in a medium-sized bowl and mix with a fork until all ingredients are incorporated. Set aside.
To make the cake batter, cream butter with the sugar until light and fluffy.
Add the egg and vanilla and beat until combined.
Toss the blueberries with 2 tablespoons of flour, then whisk together the remaining flour, baking powder, and salt.
Add the flour mixture to the batter in thirds, alternating with the buttermilk and ending with the flour. Fold in the blueberries.
Spread batter into the pan. Sprinkle batter evenly with the streusel topping.
Bake for 45 to 50 minutes until a toothpick inserted in the center comes out clean.
Let cool at least 15 minutes before serving.