Heat oven to 350 degrees
Mix butter, peanut butter, sugars, and egg
Stir in flour, oats, baking soda, and salt
Spread in greased 9x13 pan
Bake until golden brown, 17-22 minutes
Cool completely
Mix powdered sugar, peanut butter, and milk until spreading consistency
Save out ⅓ cup of frosting
Stir cocoa and milk into remaining frosting until smooth
Frost bars with cocoa frosting
Drop peanut butter frosting by spoonfuls on cocoa frosting
Swirl with a wooden skewer or knife for marbled effect
