Prep 4 serving glasses by lining the rim with a thin coating of peanut butter. Chop up the Reese's pieces and roll the peanut butter rims in them. Set aside.
Add milk, ice cream, and peanut butter to blender. Blend until smooth, about 15-20 seconds. Pour into prepped glasses, top with whipped cream, half of a peanut butter cup, a drizzle of chocolate sauce, and serve with a straw.