Preheat the oven to 350° F.
Combine flour, baking, powder, salt, and cinnamon in a medium bowl. Set aside.
In a separate bowl, whisk together egg and sugars until combined. Mix in butter and vanilla.
Add wet ingredients to dry. Mix just until combined.
Add buttermilk and stir until combined, batter will be slightly lumpy.
Thoroughly grease a 8"x8" or 9"x9" baking dish with butter or cooking spray. Spread batter into pan evenly with a spatula.
Thinly slice the 2 Tablespoons of butter and place the slices on top of the batter.
In a small bowl, combine brown sugar, white sugar, and cinnamon for topping. Sprinkle evenly on top of batter.
Bake for 20-24 minutes or until a toothpick comes out clean. Try not to over bake.
Let cool a few minutes before serving. Can be served warm or at room temperature.