Grease a heart-shaped baking pan with cooking spray.

In a large pot over low heat, melt the butter. Stir in the mini marshmallows until fully melted and smooth.

If using, add food coloring and mix until incorporated.

Remove from heat and fold in the Rice Krispies until evenly coated.

Transfer the mixture into the prepared pan and press down firmly to shape.

Allow cooling for about an hour before cutting out heart shapes.