3 tablespoons unsalted butter
4 cups miniature marshmallows
6 cups Rice Krispies cereal
2 cups white candy melts
1/4 cup red candy melts
1. Grease a 9-by-13-inch pan with cooking spray. In a 6-qt pot melt the butter. Add marshmallows and stir to coat with butter. Continue cooking and stirring over low heat until marshmallows are completely melted; remove from heat and stir in cereal.
2. Using a greased spatula or your hands, press the cereal mixture firmly into the pan. Let cool completely. Invert treats onto a cutting board.
3. Melt white and red candy melts. Transfer red melts to a zip-top bag and snip off a small corner for piping. Cut treats in half and work with one piece at a time so you can marble the candy before it sets.
4. Spread melted white candy on top of one half of the treats. Dot surface with red melts (dots should be about the size of a pea). Use a toothpick or skewer to marble. Repeat with remaining half. Allow candy to set for about 30 min before cutting with heart-shaped cutters.