Line the bottom and sides of a 9x9-inch square pan with foil, allowing it to overlap the edges; set aside.
In a large microwave-safe bowl, combine the red velvet cake mix, confectioners' sugar, milk, and the butter pieces without stirring.
Microwave the mixture on high for 2 minutes.
Remove from the microwave and immediately stir until all the butter is fully melted and the mixture is smooth.
Fold in the white chocolate chips while the mixture is still warm so they soften and create a marbled effect.
Spoon the fudge into the prepared pan and smooth it into an even layer.
If using sprinkles, scatter them over the top and press lightly so they stick.
Cover the pan with plastic wrap and refrigerate for at least 2 hours, or until firm, before lifting out with the foil and cutting into pieces.