Preheat Oven: Preheat your oven to 350°F (175°C). Grease and line a 9x13-inch baking dish with parchment paper, leaving an overhang on the sides for easy removal.

Cream Butter and Sugars: In a large mixing bowl, cream together the softened butter, granulated sugar, and brown sugar until light and fluffy. This should take about 2-3 minutes.

Add Eggs and Vanilla: Beat in the eggs one at a time, ensuring each is fully incorporated before adding the next. Stir in the vanilla extract.

Combine Dry Ingredients: In a separate bowl, whisk together the flour, baking powder, salt, and ground cinnamon. Gradually add this dry mixture to the wet mixture, mixing until just combined.

Spread Batter in Pan: Spread the batter evenly into the prepared baking dish, using a spatula to smooth the top.

Bake: Bake in the preheated oven for 25-30 minutes, or until the bars are lightly golden and a toothpick inserted into the center comes out clean.

Prepare Topping: While the bars are baking, mix together the 1/4 cup granulated sugar and 1 teaspoon ground cinnamon in a small bowl.

Add Topping: As soon as the bars come out of the oven, brush the top with the melted butter and immediately sprinkle the cinnamon-sugar mixture evenly over the top.

Cool and Slice: Allow the bars to cool completely in the pan. Use the parchment paper overhang to lift the bars out of the pan and onto a cutting board. Slice into squares or rectangles.