Preheat oven to 350° and grease a 9-x-9" pan with cooking spray.
In a large bowl using a hand mixer, beat butter and both sugars
until light and fluffy. Add eggs and vanilla and beat until
combined.
In another bowl, whisk together flour, cinnamon, baking powder,
and salt. Add dry ingredients to wet ingredients and beat until
just combined.
Press batter into prepared pan and sprinkle top with cinnamon
sugar.
Bake until golden and still slightly soft in the middle, 25 to 30
minutes.
