First, make the cake batter pieces. Combine 3/4 cup of the tempered cake mix, milk, melted butter, and salt in a medium sized bowl. Use a fork to stir together until it forms a wet dough (it will thicken as it sits!). Add the rainbow sprinkles and fold together to evenly distribute. Set aside while you make the ice cream.
In a medium bowl combine 3/4 cup of the tempered cake mix, sweetened condensed milk, vanilla, almond and salt. Use a fork to stir together until fully mixed. Set aside.
In a stand mixer fitted with the whisk attachment, beat the heavy cream on low speed, gradually increasing to high, until soft peaks form and the whipped cream holds its shape, about 1 minute. Remove the bowl from the stand mixer and add the sweetened condensed milk mixture to the cream. Use a silicone spatula to gently fold until combined and no streaks of sweetened condensed milk remain. Last, fold in the sprinkles until evenly distributed.
Spoon half of the ice cream mixture into a 1 pound loaf pan. Use a .5 ounce cookie scoop (a spoon also works!) to make small balls out of the cake batter pieces, dropping about half of them on top of the first half of the ice cream. Repeat the process, topping with the second half of the ice cream and the rest of the cake batter pieces. Use a butter knife to gently swirl everything together.
Cover tightly with plastic wrap and place in the freezer to set for at least 8 hours before serving. When tightly covered, ice cream will keep in the freezer for up to 2 months.
Notes
To temper the cake mix, line a baking sheet with parchment paper and preheat the oven to 325°F. Spread the cake mix out into an even layer. Place in the oven and bake for 2 minutes, take it out and use a rubber spatula to stir the mixture. Repeat this process for 15 minutes or until the mixture has reached 165°F. Remove frpm the oven and allow to cool before using.