Preheat oven to 350° with the oven rack in the middle position. Grease and line an 8X8 baking pan with parchment paper. Set aside.
In a mixing bowl add the melted butter, granulated sugar, and brown sugar. Mix together by hand using either a whisk or a wooden spoon until sugar is incorporated, about a minute. Add in egg and vanilla extract and mix to combine.
In a separate bowl whisk together the all purpose flour, salt, baking powder, and cinnamon. Add to the wet ingredients and gently fold to combine, being careful not to over mix.
Pour batter into prepared baking pan. In a small bowl mix together the granulated sugar and cinnamon for topping. Sprinkle over the top of the batter. Bake for 16-18 minutes. A toothpick inserted into the center should come out clean and the edges be very lightly golden brown.
After a few minutes of cooling, remove the blondies from the pan and allow to cool completely on a wire rack. When cooled completely slice into bars. Place 1/4-1/3 cup of dulce de leche into a microwave safe bowl and microwave for 15-20 seconds until warm and spreadable. Drizzle over each churro blondie. Enjoy!