Begin by preparing your workspace - line a baking tray with parchment paper and lightly coat with cooking spray to prevent sticking.
Gently melt butter in a large pot over low heat, careful not to overheat or brown it.
1 stick unsalted butter
Set aside 2 cups of marshmallows, then add the remaining marshmallows to the melted butter. Stir constantly over low heat until completely melted and smooth.
16 ounces mini marshmallows
Remove from heat immediately and stir in vanilla extract and salt until well combined.
1 teaspoon pure vanilla extract, ¼ teaspoon salt
Fold in Rice Krispies cereal until evenly coated, then add reserved marshmallows and nonpareil sprinkles. Continue folding until everything is well distributed.
8 cups Rice Krispies cereal, ¼ cup nonpareils
Spread mixture into prepared pan, pressing gently to create an even layer.
Allow treats to cool and set for 30-45 minutes before cutting into bars.
Melt chocolate wafers using a double boiler or candy melting pot until smooth.