Creating Key Lime Pie Bars – Browned Butter Blondies is straightforward. Follow these steps for success:

1. Preheat Your Oven: Start by preheating your oven to 350°F (175°C). Grease and line a 9×13-inch baking pan with parchment paper, leaving some overhang.

2. Brown the Butter: In a saucepan over medium heat, melt the unsalted butter. Continue cooking until it turns a golden-brown color and gives a nutty aroma, which should take about 5-7 minutes. Be careful not to burn it!

3. Mix the Blondie Base: In a mixing bowl, combine the browned butter and brown sugar. Stir until well blended. Let it cool slightly before adding the eggs and vanilla extract; mix until smooth.

4. Combine Dry Ingredients: In a separate bowl, whisk together the flour, baking powder, and salt. Gradually fold this into the browned butter mixture until fully combined.

5. Pour the Base into the Pan: Spread the blondie batter evenly into the prepared baking pan.

6. Bake: Place the pan in the oven and bake for 25-30 minutes, or until a toothpick inserted into the center comes out clean. Allow it to cool in the pan.

7. Prepare the Key Lime Topping: While the base cools, whisk together the sweetened condensed milk, key lime juice, egg yolks, and lime zest in a bowl until smooth.

8. Add the Topping: Once the blondie base has cooled, pour the key lime mixture evenly over the top.

9. Bake Again: Return the pan to the oven and bake for an additional 10-15 minutes until the topping is set but slightly jiggles in the center.

10. Cool & Chill: Allow the bars to cool completely at room temperature. Then, refrigerate for at least 2 hours, or until thoroughly chilled.

11. Cut into Bars: Using the overhanging parchment paper, lift the bars out of the pan and cut into squares or rectangles.