Preheat your oven to 350°F (175°C). Grease a 9x13 inch baking dish or line it with parchment paper for easy removal.
In a medium bowl, whisk together the flour, baking powder, and salt. Set aside.
In a large bowl, cream together the softened butter and 1 cup of sugar until light and fluffy. Add the eggs one at a time, mixing well after each addition. Stir in the vanilla extract.
Gradually add the dry ingredients to the wet ingredients, mixing until just combined. Do not overmix.
Spread the batter evenly into the prepared baking dish. Bake for 20-25 minutes, or until a toothpick inserted in the center comes out clean.
While the bars are baking, mix together the 1/4 cup of sugar and cinnamon in a small bowl.
Once the bars are done baking, remove them from the oven and let them cool for about 10 minutes. Brush the melted butter over the top of the warm bars, then sprinkle the cinnamon-sugar mixture evenly over the top.
Allow the bars to cool completely in the pan before cutting into squares.