Heat oven to 350°F. In small bowl, mix crust ingredients until well blended. Press in bottom of ungreased 13x9-inch pan. Bake 8 to 10 minutes or until lightly browned. Cool slightly, about 5 minutes. Increase oven temperature to 375°F.
Meanwhile, in medium bowl, mix 1 cup brown sugar, 2 tablespoons flour, the baking powder and eggs until well blended. Stir in chocolate chips and nuts. Pour topping evenly over crust, spreading slightly if necessary.
Bake 13 to 18 minutes or until deep golden brown and center is set. Cool completely, about 1 hour. For bars, cut into 6 rows by 6 rows.