3/4 cup butter or margarine
1/3 cup creamy or crunchy peanut butter
1 cup brown sugar (packed)
1 egg
1 teaspoon vanilla extract
2 cups all-purpose flour

Preheat oven to 350 degrees F (180 degrees C).

Mix all ingredients together and pat firmly into a 9 x 13-inch pan. Bake for 15 to  20 minutes. Cool before icing with chocolate peanut butter icing.

Chocolate Peanut Butter Icing
1/3 cup semisweet chocolate chips
1/2 cup creamy peanut butter

Melt chips and blend in peanut butter, spread on top of cooled cake.