1 (14-oz.) can sweetened condensed milk
1/2 c. yellow or Funfetti cake mix
2 c. white chocolate chips, melted
1/2 c. confetti rainbow sprinkles, divided
Line a 8×8 or 9×9-inch pan with parchment paper.
In a large bowl, stir together sweetened condensed milk and cake mix until combined. Fold in melted chocolate. (It may look like chocolate is seizing, but keep stirring until smooth and thick.) Gently fold in cup of sprinkles.
Pour mixture into prepared pan and smooth top with an offset spatula. Top with remaining cup sprinkles and gently press into fudge.
Refrigerate until firm, about 2 hours.
Cut into 16 pieces and serve.