Lightly grease a muffin pan with nonstick cooking spray, blotting any pools of oil with a paper towel. Set aside.
In a large stainless steel mixing bowl set over a pot of barely simmering water (making sure that the bottom of the bowl does not touch the water), melt white chocolate until smooth.
Using a 2 tablespoon measure, pour the melted chocolate into the bottom of each mold (only fill 8). Place into the refrigerator to set for 10 minutes.
Remove the muffin pan from the refrigerator. Add 1 tablespoon of marshmallows into the center of each mold. Top with 2 tablespoons of melted chocolate, making sure to cover the marshmallows. Use the back of a spoon to smooth the surface if necessary. Gently squeeze one drop of food coloring onto each mold. Use a wooden skewer to create a decorative swirl. For added effect, you can crumble some of the remaining marshmallows on top.
Refrigerate for 30 minutes until set.
Use a small offset spatula to remove the chocolate cups from the mold. Store at room temperature.