Line cookie sheets or countertop with parchment paper or foil.
In a double boiler, over medium heat, melt butter and marshmallows. Stir with a wooden spoon until completely melted and smooth. Reduce heat to low.
Add a few drops of green food color to the marshmallow mixture and stir to combine. Add additional food color to achieve the desired color.
Pour corn flakes into the marshmallow mixture and stir until completely coated.
Use a large tablespoon to drop the mixture in mounds onto the parchment paper or foil. Immediately add 3 red candies to the center of each cookie before they cool and become set.
Allow the holly cookies to cool and set up before serving or storing.
Using a double boiler prevents the butter and marshmallows from burning. It also allows you to keep the cookie mixture warm while you scoop out individual mounds and add the candies. If you don’t have a double boiler, you can make one. Simply place a heat proof bowl over a saucepan partially filled with simmering water.
Add the red candies immediately after scooping the mixture onto the parchment paper. If the mixture cools and sets up, the candies won’t stick. I keep the candies in a little bowl, so they are ready to be quickly added to the cookies.
If you don’t have parchment paper, foil or waxed paper will also work.