Maybe this is the recipe for peanut bars. It has the brown sugar and white sugar.

Peanut Bars

1 1/2 cups flour
1/4 cup butter
3/4 cup peanut butter
1/2 cup brown sugar
1 1/4 cups sugar
3 eggs
1 tsp. vanilla
1 1/2 tsp. baking powder

Mix above ingredients together. Spread onto greased baking dish. Bake at 350 for 20 min.

Icing
3 cups powdered sugar
1/4 cup peanut butter
1/4 cup milk

Mix together and spread onto warm bars.

Don't know if this is the one or not. This is the recipe that was served at my high school.
Good luck!