Browning the butter before mixing it into the batter gives these blondies a deep, nutty, caramel-like flavor that sets them apart from a standard recipe. The bars bake up chewy in the center with lightly crisp edges and come together in under an hour. They keep well at room temperature for several days.
Preheat your oven to 350°F (175°C) and line an 8x8 inch baking pan with parchment paper, allowing some overhang for easy removal.
In a medium saucepan, melt the unsalted butter over medium heat. Cook, swirling the pan occasionally, until the butter has browned and has a nutty aroma, about 5-7 minutes. Be sure to watch closely to prevent burning. Remove from heat and let it cool slightly.
In a mixing bowl, whisk together the brown sugar, granulated sugar, and browned butter until combined. Add eggs, one at a time, whisking well after each addition, then stir in the vanilla extract.
In a separate bowl, combine the flour, baking powder, and salt. Gradually add this dry mixture to the wet ingredients, folding gently with a rubber spatula until just combined.
Fold in the chopped nuts. Spread the batter evenly into the prepared baking pan and smooth the top.
Bake for 25-30 minutes, or until a toothpick inserted into the center comes out mostly clean with a few moist crumbs. Cool completely in the pan on a rack before cutting into bars.
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Notes
For an extra layer of flavor, you can mix in 1/2 cup of chocolate chips or a sprinkle of sea salt on top before baking.
If you prefer less sweetness, reducing the granulated sugar by 1/4 cup will result in a less sweet but equally delicious bar.