Creating these Key Lime Pie Bars is a delightful process. Follow these steps to achieve delicious results:

1. Preheat your Oven: Set your oven to 350°F (175°C) and grease a 9×13-inch baking dish.
2. Brown the Butter: In a saucepan, melt the unsalted butter over medium heat. Continue cooking until the butter turns golden brown and develops a nutty aroma. Remove from heat and allow to cool slightly.
3. Mix Sugars: In a large mixing bowl, combine the granulated sugar and brown sugar. Stir in the browned butter until well combined.
4. Add Eggs and Vanilla: Beat in the eggs and vanilla extract until the mixture is smooth and creamy.
5. Incorporate Dry Ingredients: Gently fold in the flour, baking powder, and salt until just combined, being careful not to overmix.
6. Add Key Lime Flavor: Stir in the freshly squeezed key lime juice and zest until distributed evenly throughout the batter.
7. Bake: Pour the batter into the greased baking dish and bake for 25 minutes, or until a toothpick inserted into the center comes out clean. Allow to cool completely before dusting with powdered sugar and slicing.

These steps will guide you through making the most luscious Key Lime Pie Bars ever.