Spread butter in a 9 x 9-inch baking dish, then line it with parchment paper.
In a medium saucepan, heat the chocolate chips and sweetened condensed milk over low heat while stirring constantly. Stir until the chocolate chips are completely melted, then remove from heat.
Add in the marshmallows, peanuts, and chocolate candies. Stir to combine.
2 cups mini marshmallows, 1 cup salted peanuts, 1 cup M&Ms
Pour the mixture into the prepared baking dish, and use a spatula to spread the fudge into an even layer.
Top the fudge with red and green sprinkles if using. Gently press the sprinkles into the fudge.
2 tablespoons holiday sprinkles
Allow the fudge to set completely before cutting. This takes about 2 hours in the refrigerator or 4 hours at room temperature. Store the fudge in an airtight container for up to 3 days.
Notes
The calories listed are an approximation based on the ingredients and a serving size of 1/16th the total recipe (1 square of fudge after it has been cut into 16 equal sized pieces). Actual calories will vary. The red and green sprinkles are optional. The fudge can be stored in a sealed container for up to 3-days.