Put the mini marshmallows in a large, microwave-safe bowl. Pour the melted butter over the mini marshmallows and stir to coat.

Microwave for 1 minute and 30 seconds, stirring after 45 seconds, until smooth.

Stir in the red gel food coloring.

Add the rice krispies and stir until coated.

Press into a parchment-lined (or well-greased) rimmed baking sheet (about 16x12x1).

Turn out onto a large piece of parchment paper.

Spread buttercream frosting over rice krispies treats and top with sprinkles if desired.

Starting at the short side of the bars, slowly roll the bars up, gently pressing closed any cracks or holes that may form.

Chill until firm and use a serrated knife to cut into 1-inch segments.

Store in the refrigerator in an airtight container.