Chango Bars

This is a recipe from Sierra's class.  It was in a book they read...she really wants me to make them :)

1/2 cup butter
1/2 cup margarine
2 cups brown sugar
3 eggs
2 1/3 cups flour
1 TBL baking powder
1 tsp salt
1 cup chocolate chips
1 cup mixed nuts

Melt butter and margarine.  While this is melting, cream brown sugar and eggs, then add melted butter and margarine.  Combine flour, baking powder, and salt and stir into sugar mixture.  Fold in chocolate chips and nuts.  Pour mixture into greased 9x13 pan and bake 45-50 minutes at 350 degrees.