Preheat your oven to 350°F (175°C) and grease a 9x13-inch baking pan.
In a large mixing bowl, combine the melted butter, brown sugar, and granulated sugar. Mix well until smooth.
Add the eggs and vanilla extract, stirring until fully incorporated.
In a separate bowl, whisk together the flour, baking powder, baking soda, salt, and ground cinnamon.
Gradually add the dry ingredients to the wet mixture, stirring until just combined.
Pour the batter into the prepared baking pan, spreading it evenly.
In a small bowl, mix the 1/4 cup of granulated sugar with an additional teaspoon of cinnamon. Sprinkle this mixture evenly over the top of the batter.
Bake for 25-30 minutes, or until a toothpick inserted in the center comes out clean.
Allow the blondies to cool in the pan for at least 10 minutes before cutting into squares.