Preheat the oven to 350 degrees F. Butter a 9 inch square baking pan.

In a large saucepan over medium high heat, melt the butter until it turns golden brown, about 5 minutes. Remove from heat and let cool. The butter will continue browning once it is off the heat.

In a medium bowl, combine the flour, baking powder and salt.

Pour the brown butter through a fine mesh strainer into a large bowl. Add both sugars and beat in the eggs and vanilla extract. Gently fold in the dry ingredients until just combined and then add the white chocolate chunks and nuts.

Spread the dough into the prepared baking pan. Bake for 30-35 minutes until the blondies are golden brown. Cool completely before cutting into squares.

Store in an airtight container.