In a medium bowl, combine the sugar, flour, and cinnamon.

Cut in the butter with a pastry blender or your fingers until the mixture resembles coarse crumbles. Refrigerate until ready to use.

Preheat the oven to 350 degrees.

Spray a 9x9 baking dish with cooking spray.

In a medium bowl, stir together the flour, baking powder, and salt. Set aside.

Add softened butter and sugar to a large bowl and using a mixer cream until light and fluffy, about 4 minutes. Scrape the sides down.

Add the egg, milk, and vanilla and mix on low speed until the ingredients start coming together.

With the mixer running, add the flour mixture, mixing until fully incorporated.

Spread the batter in the prepared baking dish then sprinkle the streusel over the batter evenly.

Bake until cooked through, about for 30-35 minutes.

Cut into squares and serve warm or at room temp.