In a small bowl, whisk egg yolks. Pour one cup heavy cream in a medium bowl, with mesh strainer set on top.

In a medium saucepan, combine whole milk, remaining 1 cup heavy cream, sugar, salt, vanilla and cake mix. Cook over medium-low heat, stirring until smooth and then occasionally, until heated through and just steaming.

While whisking the yolks continuously, slowly drizzle a quarter of the hot liquid into the yolks. Pour egg mixture into saucepan. Continue cooking until the mixture coats the back of a wooden spoon.

Pour through mesh strainer into heavy cream. Cool over an ice bath. Transfer to the refrigerator to chill completely prior to churning, 4-6 hours or overnight.

Churn according to manufacturer's directions. In the last 5 minutes of churning, slowly add rainbow sprinkles. Transfer to a freezer safe container. Freeze until solid.