?Mix butter, powdered sugar, and vanilla in a large bowl with a hand mixer. Divide into two equal portions. Transfer half to another bowl.
Add peanut butter to one half of frosting and mix with a hand mixer. Add 1-2 tablespoons of milk to get desired spreading consistency.
Add Nutella to remaining half of frosting and beat with hand mixer. Add 1-2 tablespoons of milk to get desired spreading consistency.
Spread peanut butter frosting on one slice of “bread.” Top with Nutella frosting and second slice of bread. Wrap in plastic and chill until firmed up. Repeat with remaining bread and frosting.