Preheat oven to 350 degrees F (177 degrees C).  Butter an 8 inch (20 cm) spring form pan and line the bottom of  the pan with parchment paper.  Set aside.

For streusel topping:  In a large bowl, mix together the flour, sugar, and ground cinnamon.  Cut in the butter with a pastry blender or fork until it resembles coarse crumbs.  Set aside while you make the cake batter.

In a separate bowl whisk together the flour, baking powder, and salt.  Set aside.

In the bowl of your electric mixer, with the paddle attachment, cream the butter.  Add the sugar and beat until light and fluffy.  Add the egg and vanilla and beat until incorporated.  Add the flour mixture, alternately with the milk, and beat only until combined.  Spread the batter onto the bottom of the prepared pan, smoothing the top with an offset spatula. 

Evenly arrange the blueberries on top of the cake batter and then sprinkle with the streusel topping.

Bake for about 45 - 50 minutes or until a toothpick inserted in the center of the cake comes out clean.  Remove from oven and place on a wire rack to cool slightly. 

Serve warm or at room temperature.

Makes 8 - 10 servings.