Preheat oven to 180 degrees C. Grease one 20x30cm baking dish.
Cream the butter and 1 cup of the dark brown sugar together until light and fluffy. Mix in 1 beaten egg then add the flour and until well combined. Pour batter into the prepared pan and spread evenly.
Cover the batter with the remaining well-beaten egg. Sprinkle 1/2 cup of the dark brown sugar over the surface then sprinkle with the chopped pecans and top with the remaining 1/2 cup of dark brown sugar.
Bake at 180 degrees C for 35 minutes. Let cool for 30 minutes then cut into squares.