Preheat oven to 350 degrees. In a bowl, cream the butter, shortening and confectioners sugar, and add the flour to make a dough. Press into a 12 x 12-inch plain baking dish. Bake for 15 minutes, then remove from oven. While it's baking, mix eggs, brown sugar, vanilla, salt, baking powder, 2 tablespoons of flour and the pecans. As soon as you remove the cookie layer, spread the topping over the top and return to oven for 20 more minutes. If desired, sprinkle your additional topping as soon as you remove the bars from the oven. Let cool completely and cut into 1-inch bars.