In a saucepan, combine the chocolate chips, condensed milk, and butter over low heat. Stir constantly until fully melted and smooth.

Remove from heat and mix in the vanilla extract.

Pour the mixture into a lined 8x8-inch (20x20 cm) baking pan.

Smooth the top with a spatula and add holiday-themed sprinkles.

Let the fudge cool at room temperature, then refrigerate for 1-2 hours or until firm. Cut into squares and serve.