Line a sheet pan with parchment paper or a silicone baking mat.

Place the marshmallows and butter in a large microwave-safe bowl. Microwave in 30-second increments, stirring in between, until melted and smooth.

Stir in the green gel or liquid food coloring and vanilla extract until the mixture is uniformly colored and smooth.

Add the cornflakes and gently fold into the marshmallow mixture until evenly coated.

Lightly grease a 1/4 cup measuring cup with cooking spray. Pack the cereal mixture into the cup, then turn it out onto the lined sheet pan. Create a hole in the center to form a wreath shape.

Place red hot candies or red candy-coated chocolates around the wreath.

Allow the wreaths to cool completely at room temperature until firm.