I have a recipe that is very similar but has less butter (1/4 cup) and less vanilla (1/2 t). Here is the one I use:
1/4 Cup butter
1 Cup flour
1 Cup brown sugar
1 tsp baking powder
1 egg
1/2 tsp salt
1/2 tsp vanilla
Same mixing method as yours (the batter will be very thick) and same...