Preheat oven to 350 degrees F (175 degrees C). Grease an 8x8 inch square baking pan.
In a medium bowl, cream together the butter, brown sugar, and white sugar. Beat in the eggs and vanilla. Stir in the flour and pecans until just blended. Spread the mixture evenly into the prepared pan.
Bake for 35 to 40 minutes in the preheated oven, or until edges begin to pull away from the sides of the pan. Allow bars to cool in the pan before cutting.