Preheat oven to 350°F. Grease a 9×13 inch baking pan and set aside.
Stir together butter and brown sugar. Add in eggs and vanilla and stir to combine. Stir in flour, baking powder and salt. Add in nuts and stir to combine.
Spread mixture in baking pan. Bake for 30 to 33 minutes or until a toothpick comes out clean. Let cool before cutting into squares.