Preheat oven to 375 degrees F. and melt butter in 9 X 13 pan.
Put brown sugar in large mixer bowl and pour melted butter over it. Cream butter and sugar and then beat in eggs. Mix in flour, baking powder, vanilla and pecans and pour back into already greased pan.
Bake 25 to 30 minutes, or until brownies begin to pull away from sides of pan. When cool cut into squares or bars.