Whisk together the sugar and yellow cake mix in a large mixing bowl.
¾ cup sugar, ⅔ cup yellow cake mix
Add the cream, milk, and vanilla extract, beating with an electric hand mixer until combined.
2 cup heavy cream, 2 cup whole milk, 2 teaspoon vanilla extract
Pour the birthday cake ice cream base into the ice cream maker freezer bowl and set program to "ice cream" mode, or follow the manufacturer's instructions for churning ice cream.
Just before the churning cycle ends, add ¼ cup of rainbow sprinkles and let the last minute or two of the churn cycle complete.
¼ cup rainbow sprinkles
Remove the dasher, scraping the ice cream back into the freezer bowl.
Crumble the two frosted cupcakes up into small pieces.
2 vanilla frosted cupcakes
Transfer half of the ice cream to an insulated ice cream storage container, or lined loaf pan, and distribute half the crumbled cupcakes mixture and 2 tablespoons of rainbow sprinkles on top of the ice cream.
¼ cup rainbow sprinkles
Repeat with the remaining half of the ice cream, crumbled cupcakes, and the last 2 tablespoons of rainbow sprinkles.
Cover the insulated ice cream tub and set in your freezer for the 'hardening' stage, about 2 hours. PRO TIP: You can of course enjoy your Funfetti ice cream while in this soft serve stage also, but it will take the hardening stage to make it firm enough to scoop into balls.