Preheat your oven to 350°F (175°C) and prepare an 8x8 inch baking pan with parchment paper.

Melt the butter in a large mixing bowl and whisk in the brown and white sugars until smooth and creamy.

Sift in the flour, baking powder, and cinnamon to the butter-sugar mixture, stirring gently until just combined.

Pour half the batter into the prepared pan, sprinkle with cinnamon sugar, then layer the remaining batter and swirl gently.

Bake for 30 to 38 minutes until edges are golden brown and center is slightly underdone.

Cool in the pan for 15 minutes, then transfer to a wire rack to cool completely.

Mix the powdered sugar, cream cheese, and milk to create the frosting, then spread it over the cooled blondies.

Slice into squares and serve.