Preheat your oven to 350°F (175°C) and lightly grease a baking dish.

In a large bowl, whisk together the melted butter, brown sugar, and granulated sugar until well blended and glossy.

Incorporate the eggs and vanilla extract, mixing until smooth.

In a separate bowl, whisk together the flour, baking powder, salt, and cinnamon.

Gradually add the dry ingredients to the wet ingredients, mixing just until combined.

Pour the mixture into the prepared baking dish and smooth it out evenly.

In a small bowl, mix the additional granulated sugar and cinnamon together, then sprinkle over the batter.

Bake for 20-25 minutes, or until a toothpick inserted in the center comes out clean.

Let cool before slicing into squares.