Preheat the oven to 350 degrees F.

Butter a springform baking pan and dust with flour, tapping out excess. Set aside.

In a medium bowl, sift together the flour, baking powder, and salt; set aside.

In the bowl of an electric mixer fitted with the paddle attachment, cream butter and sugar on medium speed until light and fluffy, about 3 minutes. Reduce mixer speed to low, and add egg and vanilla, beating until fully combined.

Add reserved flour mixture, alternating with the milk, a little of each at a time, starting and ending with the flour mixture. Remove from mixer. Gently fold in blueberries.

Pour batter into prepared pan; sprinkle topping over cake. Bake until cake tester comes out batter-free, 60 to 70 minutes. Transfer to a wire rack to cool 10 minutes. Remove from pan; cool 15 minutes before serving.

Streusel Topping:
1 cup all-purpose flour
1/4 cup packed light-brown sugar
1 teaspoon ground cinnamon
1/4 teaspoon salt
6 tablespoons unsalted butter, room temperature

In a medium bowl, combine flour, sugar, cinnamon, and salt. Using a pastry blender, or a fork, cut in the butter until fine crumbs form.

Using hands, squeeze together most of the mixture to form large clumps. Can be frozen in an airtight container for up to 6 months.