Preheat your oven to 350°F (175°C).
Grease a 9x13-inch baking pan with butter or cooking spray.
In a separate bowl, whisk together the dry ingredients: flour, baking powder, baking soda, and salt.
In a large mixing bowl, combine melted butter, brown sugar, and granulated sugar. Mix until smooth and creamy.
Add eggs and vanilla extract to the butter and sugar mixture. Stir until well combined. Gradually add the dry ingredients and mix gently until just combined.
Mix together cinnamon and granulated sugar for topping. Spread the blondie batter into the prepared baking pan and sprinkle the cinnamon-sugar mixture over the top.
Bake for 20-25 minutes. Check for doneness with a toothpick.
Let the blondies cool in the pan for at least 10 minutes before transferring to a wire rack to cool completely. Cut into squares and enjoy.