• Preheat oven to 350 degrees. Butter baking dish and set aside.
• Mix softened butter, both sugars, and peanut butter in a large mixing bowl. (You can use crunchy or smooth peanut butter.) Add the eggs and vanilla and combine thoroughly. Add the flour, oats, and baking powder, then mix well.
• Press batter into the prepare baking dish. Bake for 15 minutes, or until a very light brown. (Don't overbake.) Let cool.

Peanut Butter Frosting

• While the bars are baking, add 1/2 cup butter and 1/2 c. peanut butter to a large saucepan. Melt over medium heat, stirring until smooth, then remove from stove. Add 2-3 tablespoons milk, then slowly add the powdered sugar. If I's too thick, add a bit more milk until the desired consistency. Mix well to get out all the lumps.
• Spread the frosting over the cake, spreading evenly to the edges.