Stir the sweetened condensed milk, dry cake mix, and vanilla in a large bowl. Set aside.
Whip the heavy cream in a chilled bowl until stiff peeks form, about 3 to 5 minutes.
Gently fold the whipped cream into the milk mixture, stirring until just combined.
Add sprinkles, if using, folding until just incorporated.
Pour into a large air tight container.
Freeze for 3 to 4 hours or overnight.
Notes
While this isn’t absolutely necessary, you can add even more flavor by stirring in a 1/4 teaspoon of butter and 1 teaspoon vanilla extract.
Another fun addition? Fold in baked cake pieces! Bake the cake and cool completely. Cut into small pieces. Freeze solid before folding in.
Spread canned frosting onto a baking tray lined with parchment. Freeze solid. Break into small pieces and sprinkle throughout the better before freezing.