Harvard Squares

1 cup softened unsalted butter
3/4 cup firmly packed brown sugar
3/4 cup white sugar
2 large eggs
1/2 tsp. vanilla
2 1/4 cups flour
1 tsp. baking soda
1/2 tsp. salt
1 cup chocolate chips
1 cup peanut butter chips or butterscotch chips (See above comment)

Preheat the oven to 350 degrees F.  Cream the butter, then add the sugars and beat until fluffy.  Add the eggs and vanilla, mixing well.  Combine the flour, baking soda, and salt, then add to the batter.  Combine the chocolate chips and other chips.  Stir them into the batter.

Spread the batter evenly into a well-greased jelly-roll pan (approximately 15 1/2 inches by 10 1/2 inches). 

Bake in the oven until golden brown, 25 to 30 minutes.  Cool in the pan, then cut into squares.  Makes 48 squares.