Begin by preheating your oven to 350 degrees F. Line a 9-inch square baking pan with parchment paper. Spray with baking spray and set aside.
In a large bowl, whisk together the flour, ground cinnamon, baking powder, baking soda, and salt. Set aside.
In a medium saucepan, add the butter and brown sugar. Cook and stir until the butter is melted and the mixture is smooth. Remove from the heat and allow to cool slightly. Stir in the eggs and vanilla extract.
Add this mixture to the flour mixture and stir until combined.
Spread the batter in the prepared baking pan. Bake for 24-28 minutes or until a toothpick inserted near the center comes out clean.
For the topping:
In a small bowl, mix together the granulated sugar and cinnamon.
While the bars are still warm, brush them evenly with the melted butter, then sprinkle with the cinnamon-sugar mixture.
Allow to cool completely before slicing and serving.
Pack and store leftovers in an airtight container.