Butter a 9x13 inch baking dish and set it aside.

In a microwave-safe bowl, melt marshmallows in 20-second increments, twice, until slightly melted.

Set aside, then in another microwave-safe bowl, melt butter in 20-second increments until nearly all melted.

Combine melted butter with marshmallows and microwave again for about 20 seconds.

Stir to mix them well.

Add food coloring and Rice Krispies, stirring to combine.

Mix in Lucky Charms, stirring until fully coated.

Using a buttered rubber spatula, spread the mixture evenly into the baking dish.

Sprinkle additional marshmallows on top.

Refrigerate for 30 minutes.

Cut into 12 squares, or 8 squares for larger treats.