1 (14-ounce) can sweetened condensed milk
1 (12-ounce) bag white chocolate chips
1 cup white cake mix
1/3 cup sprinkles, plus more for topping
Line an 8x8-inch baking pan with parchment or wax paper.
In a medium saucepan, combine the condensed milk and white chocolate. Cook over low heat, stirring constantly, until the chocolate is melted. Remove from the heat and stir in the cake mix. The mixture may start to firm up; this is okay. Gently fold in the sprinkles.
Pour the fudge into the prepared pan. Use a rubber spatula to smooth and flatten the top. Top the fudge with extra sprinkles, if you like. Transfer the fudge to the refrigerator to set for about 2 hours. Once chilled, remove from the fridge and cut into two-inch pieces.