Place the butter in a large pot over medium heat. Add several drops of red food coloring and stir occasionally until the butter is completely melted. Add the mini marshmallows to the pot and cook, stirring constantly, until melted. Add more red food coloring until you reach your desired color.
Once the marshmallows have completely melted, remove from the heat and add the rice krispies and stir until evenly coated with the melted marshmallows Coat a large 9 x 13 baking dish with cooking spray then pour the mixture into the baking dish. Spray a piece of wax paper with cooking spray, then use the paper to mash the rice krispie treats down into the dish evenly.
Let it cool for 5 minutes before using cooking cutters to cut into heart shapes. Decorate with gel frosting and sprinkles.