Preheat the oven to 350°F (175°C) and line a 9x9 inch baking pan with parchment paper.

In a mixing bowl, whisk together the melted butter and brown sugar until smooth.

Add the egg and vanilla extract, mixing until fully incorporated.

In a separate bowl, combine the flour, baking powder, and salt. Gradually add to the wet ingredients, stirring until just combined.

In a small bowl, mix together the granulated sugar and ground cinnamon.

Pour half of the blondie batter into the prepared pan and spread evenly.

Sprinkle half of the cinnamon sugar mixture over the batter.

Add the remaining blondie batter on top and swirl with a knife. Top with the remaining cinnamon sugar.

Bake in the preheated oven for 25-30 minutes or until a toothpick inserted in the center comes out clean.

Allow to cool in the pan for 10 minutes before transferring to a wire rack to cool completely.

In a mixing bowl, beat together the softened cream cheese and butter until creamy.

Gradually add powdered sugar and vanilla extract, mixing until smooth.

Spread the frosting over the cooled blondies if desired.