Line two large baking sheets with parchment paper or wax paper.
In a large pot or Dutch oven, melt the stick of unsalted butter over low heat.
Add the entire bag of mini marshmallows. Stir continuously over low heat until the marshmallows are completely melted, smooth, and free of lumps.
Remove the pot from the heat source. Stir in the vanilla extract and green food coloring until the marshmallow mixture is a uniform holiday green.
Gently fold in the cornflakes cereal using a rubber spatula until all the flakes are evenly coated in the green marshmallow mixture.
Drop generous spoonfuls of the coated cereal onto the prepared baking sheets.
Lightly butter your fingers, then shape each warm mound into a 2-inch circle with a hole in the center to form a wreath.
Immediately press 3 to 4 red candies into the top of each wreath to resemble holly berries.
Let the wreaths set completely at room temperature for about 1 hour before serving.