Step 1: Prepare
Preheat oven to 350°F (175°C). Line a 9x13-inch baking pan with parchment paper, leaving overhang on the sides for easy removal.
Step 2: Mix Dry Ingredients
In a medium bowl, whisk together flour, baking powder, salt, and 1 1/2 teaspoons of cinnamon until well combined.
Step 3: Combine Wet Ingredients
In a large bowl, whisk together melted butter and 1 1/2 cups sugar until smooth and creamy (about 1 minute). Add eggs one at a time, beating well after each addition. Stir in vanilla extract.
Step 4: Combine
Gradually fold the dry ingredients into the wet mixture using a spatula. Mix just until no flour streaks remain. Do not overmix.
Step 5: Spread Batter
Pour batter into prepared pan and spread evenly with a spatula, making sure it reaches all corners.
Step 6: Add Topping
In a small bowl, mix remaining 2 tablespoons sugar with 1/2 teaspoon cinnamon. Sprinkle evenly over the batter. Optional: drag a knife through gently for a swirl effect.
Step 7: Bake
Bake for 22-25 minutes, until edges are golden and a toothpick inserted in the center comes out clean or with a few moist crumbs.
Step 8: Cool and Slice
Let bars cool completely in the pan (about 1 hour). Use parchment overhang to lift bars out. Cut into 16 squares with a sharp knife.