Creating Key Lime Pie Bars – Browned Butter Blondie involves a few straightforward steps:

1. Preheat the Oven: Preheat your oven to 350°F (175°C). Line a 9×13 inch baking pan with parchment paper, leaving an overhang for easy removal.

2. Brown the Butter: In a medium saucepan, melt the butter over medium heat. Continue to cook, stirring frequently, until the butter turns a light golden brown and has a nutty aroma. This should take about 5-7 minutes. Remove from heat and allow to cool slightly.

3. Mix Blondie Ingredients: In a large bowl, combine the browned butter, brown sugar, and granulated sugar. Mix well. Then, add the eggs and vanilla extract, stirring until well combined.

4. Combine Dry Ingredients: In another bowl, whisk together the flour, baking powder, and salt.

5. Combine Mixtures: Gradually add the dry ingredients to the wet ingredients, stirring just until combined.

6. Bake the Blondie Base: Pour the blondie batter into the prepared baking pan, spreading it evenly. Bake in the preheated oven for about 25-30 minutes, or until a toothpick inserted in the center comes out mostly clean. Allow to cool slightly.

7. Prepare Key Lime Filling: In a separate bowl, mix together the sweetened condensed milk, key lime juice, egg yolks, key lime zest, and a pinch of salt until smooth.

8. Add Filling to Base: Pour the key lime filling over the slightly cooled blondie base, spreading it evenly.

9. Bake Again: Return the pan to the oven and bake for an additional 15-20 minutes, or until the filling is set.

10. Cool and Chill: Remove from the oven and let it cool at room temperature for about an hour. Once cooled, refrigerate for at least 2 hours before slicing.

11. Slice and Serve: Once fully chilled, lift the bars out of the pan using the parchment overhang. Cut into squares and garnish with whipped cream and lime wedges if desired.