Line an 8-inch square baking pan with parchment paper, leaving paper overhanging on two sides. The overhang will act as a sling so the chilled fudge can be lifted out easily.

Place the white chocolate chips and sweetened condensed milk in a microwave-safe bowl. Microwave in 30-second intervals, stirring very well after each interval, until smooth; the melting process usually takes 1 1/2–2 1/2 minutes depending on the microwave.

Stir the vanilla extract into the warm fudge mixture. Divide the mixture between two bowls, leaving one portion white and tinting the other portion green with approximately 5–10 drops of gel food coloring.

Spoon alternating portions of white and green fudge into the parchment-lined pan. Run a knife or skewer through the mixture several times to create pretty ribbons, taking care not to over-swirl.

Press the red heart sprinkles or candy hearts over the top while the fudge is still soft. Add optional green or red Christmas sprinkles if desired.

Refrigerate the pan until the fudge is firm, usually 2–4 hours. Lift it out using the parchment paper, then cut it into approximately 36 small squares with a sharp knife.