Prepare a 9 X 13 pan by spraying with a non-stick cooking spray or by greasing and flouring.
Mix melted butter and brown sugar in a large mixing bowl and stir until well combined.
Add the eggs and the vanilla and mix well.
Add flour, baking powder, and pecans to the butter and sugar and mix until there are no white streaks left of flour left. Make sure and scrape the sides of the bowl often.
Pour mixture into the prepared baking pan.
Place into the preheated oven and bake for 20 to 25 minutes or until the edges begin to brown.
Remove from the oven and allow to cool before cutting into bars.
Notes
More nuts or chocolate chips can be added to this recipe. You may need to increase the baking time by 5 minutes or so.