Line a 9x13 baking pan with non-stick foil or line with aluminum foil and then butter the pan.
Place chocolate chips, butterscotch chips and peanut butter in a large, microwave safe bowl and microwave in 30 second increments, stirring after each, until completely melted and smooth.
Stove top- Place chocolate chips, butterscotch chips and peanut butter in a large saucepan over low heat. Stirring frequently heat until completely melted and smooth. Remove from heat.
Add in marshmallow and stir until the marshmallows are evenly coated.
Spread the mixture into your prepared pan.
Sprinkle with M&M’s
Refrigerate for at least 2 hours.
Remove from refrigerator and allow to sit for about 10 minutes before cutting. Cut into 24 squares and serve.
Keep any leftover in an airtight container in the refrigerator.
Notes
S'mores Bars: To make these peanut butter & marshmallow squares have a s'mores flavor, add crushed graham crackers when coating the marshmallows in chocolate.
Microwave: If you don't want to make this recipe on the stove top, you can also microwave the chocolate chips, butterscotch chips, and peanut butter in a large microwave safe bowling
Peanut Butter M&M's: For a some extra flavor, you could top this peanut butter & marshmallow squares with peanut butter or caramel filled M&M's.