Creating these luscious Key Lime Pie Bars – Browned Butter Blondie involves several straightforward steps:

1. Preheat the oven: Set your oven to 350°F (175°C). Grease a 9×9 inch baking pan or line it with parchment paper for easy removal.

2. Brown the butter: In a medium saucepan, melt 1 cup of unsalted butter over medium heat. Stir frequently until it turns golden brown and develops a nutty aroma. Remove from heat and let it cool slightly.

3. Mix the blondie base: In a large bowl, combine the browned butter and brown sugar. Mix well until smooth. Add the eggs one at a time, followed by the vanilla extract, stirring to combine.

4. Add dry ingredients: In a separate bowl, whisk together the flour, baking powder, and salt. Gradually add this mixture to the wet ingredients, mixing until just combined. Fold in the lime zest.

5. Bake the base: Pour the blondie mixture into the prepared baking pan, spreading it evenly. Bake in the preheated oven for 25-30 minutes or until golden brown and a toothpick comes out clean.

6. Prepare the key lime filling: While the blondies bake, whisk together the key lime juice and sweetened condensed milk in a bowl until well mixed.

7. Add key lime filling: Remove the blondies from the oven once baked. Pour the key lime mixture over the top while it’s still warm. Return to the oven and bake for an additional 10-12 minutes.

8. Cool completely: Allow the bars to cool in the pan on a wire rack, then refrigerate for at least 2 hours before cutting into squares.