Preheat oven to 350 degrees. Line a 9x13 inch pan with parchment paper.
Combine the 2 1/2 cups flour, baking powder, and salt in a large bowl.
In a large high walled pan or pot, melt the butter. Cook, stirring occasionally for 5-8 minutes, or until browned. Pour into a large bowl.
Mix the brown sugar into the hot butter. Set aside to cool for 10 minutes.
Whisk eggs in a small bowl. Slowly pour into the cooled butter mixture, whipping constantly. Add vanilla.
Add the dry ingredients and gently fold together.
In a bowl, combine the chocolate, nuts, and 1 TBSP flour. Add to the batter and fold in.
Pour into prepared pan. Bake for 40-45 minutes, or until a toothpick inserted in the center comes out with light crumbs. It should feel set, but soft.
Cool completely in pan. Cut into squares, and enjoy!
