Step 1: Prepare Your Pan

1. Line an 8×8-inch baking pan with parchment paper, leaving some overhang for easy removal. Lightly grease the paper with non-stick spray or butter.

Step 2: Make the Chocolate Base Layer

1. In a medium saucepan, combine the semi-sweet chocolate chips, 1 cup of sweetened condensed milk, and 2 tablespoons of butter.
2. Heat over low heat, stirring constantly, until the mixture is smooth and fully melted.
3. Remove from heat and stir in the vanilla extract. Pour the mixture evenly into the prepared pan, spreading it out with a spatula.

Step 3: Prepare the White Chocolate Swirl

1. In a separate saucepan, combine the white chocolate chips, the remaining sweetened condensed milk, and 1 tablespoon of butter. Heat over low heat, stirring until melted and smooth.
2. Divide the melted white chocolate into three bowls. Leave one bowl white, and color the others with red and green food coloring, stirring until the colors are vibrant.

Step 4: Create the Swirls

1. Spoon the white, red, and green melted chocolate randomly over the chocolate base.
2. Use a toothpick or skewer to swirl the colors together, creating a marbled effect. Work quickly before the chocolate begins to set.

Step 5: Add Toppings

1. Sprinkle crushed candy canes, festive sprinkles, or edible glitter over the top of the fudge for added texture and holiday flair.

Step 6: Chill and Set

1. Place the pan in the refrigerator and chill for 2-3 hours, or until the fudge is firm.

Step 7: Slice and Serve

1. Once set, lift the fudge out of the pan using the parchment paper overhang. Cut into 36 squares using a sharp knife, wiping the blade clean between cuts for neat edges.
2. Serve immediately or store in an airtight container.