Peanut Butter Squares

I got this from my friend Sarah Sparks' blog! It looks yummy!
Peanut Butter Squares
1/2 cup granulated sugar
1/2 cup packed brown sugar
1/2 cup butter or margarine, softened
1/3 cup peanut butter
1 egg
1 cup all-purpose flour
1 cup old-fashioned oats
1/2 teaspoon baking soda
1/4 teaspoon salt
3 tablespoons unsweetened baking cocoa
1 tablespoon milk

Peanut Butter Frosting
1 1/2 cups powdered sugar
1/4 cup crunchy peanut butter
2 to 2 1/2 tablespoons milk

1. Heat oven to 350°F. Grease 13x9-inch pan.

2. In large bowl, beat granulated and brown sugars, butter, 1/3 cup peanut butter and the egg with electric mixer on medium speed. Stir in flour, oats, baking soda and salt. Spread in pan.

3. Bake 17 to 22 minutes or until golden brown. Cool completely on wire rack, about 15 minutes.

4. Meanwhile, mix all Peanut Butter Frosting ingredients until smooth and spreadable; reserve 1/3 cup. Stir cocoa and 1 tablespoon milk into remaining frosting until smooth. If necessary, stir in additional milk until spreadable.

5. Spread cooled bars with cocoa frosting. Drop Peanut Butter Frosting by teaspoonfuls onto cocoa frosting; swirl through frostings for marbled design. For squares, cut into 8 rows by 6 rows.