Start by lining your 8×8-inch baking pan with parchment paper, leaving a little overhang on the sides. This makes lifting the fudge out much easier once it’s chilled. Lightly grease it if you’d like extra insurance against sticking.
In a microwave-safe bowl, combine the semi-sweet chocolate chips and half of the sweetened condensed milk. Heat in 30-second bursts, stirring after each until smooth. Add a teaspoon of vanilla extract and stir again. Pour this rich chocolate layer into your prepared pan and spread evenly.
Now, repeat the same process with the white chocolate chips and the remaining condensed milk. Melt and stir until silky, then add in the rest of the vanilla extract. Pour the white chocolate mixture over the semi-sweet layer and gently spread to cover evenly.
While the top is still soft, scatter the Christmas sprinkles evenly over the surface. Gently press them in with the back of a spoon so they stick nicely once set.
Place the pan in the refrigerator and let it chill for at least one hour—or until the fudge is firm. Once set, lift it out using the parchment paper and cut into small squares with a sharp knife. Keep the pieces small—this fudge is rich!