Add 4 cups white chocolate chips to a large microwave-safe bowl. Heat them in the microwave in 30-second increments, stirring after every increment until fully melted and smooth.
Stir ½ cup marshmallows into the melted white chocolate, then heat for 30 additional seconds.
Add 4 cups chow mein noodles and ½ cup peanuts, if desired, and stir until everything is evenly coated. Scoop the cookies in 2-tablespoon portions onto a piece of parchment paper. Immediately top with sprinkles, if desired.
Chocolate Haystacks
Add 4 cups white chocolate chips, 2 cups butterscotch chips, and ¼ cup peanut butter to a large microwave-safe bowl. Heat them in the microwave in 30-second increments, stirring after every increment until fully melted and smooth.
Add ½ cup peanuts and stir until everything is evenly coated. Scoop the cookies in 2-tablespoon portions onto a piece of parchment paper. Immediately top with sprinkles, if desired.