In medium bowl, mix 2 1/2 cups flour, the baking powder and salt; set aside. In 2-quart saucepan, cook brown sugar and butter over medium heat, stirring frequently, until butter is melted. Remove from heat; cool slightly. Add eggs, one at a time, beating until blended after each addition. Stir in flour mixture. Stir in peanut brittle and vanilla. Press dough in baking dish.