Fold gently. When adding the sweetened condensed milk to the whipped heavy cream, gently fold to keep the mixture somewhat airy. Fold and mix until it is thoroughly combines but still fluffy.
Don't over mix the creams! When pulling your butter knife through the three colors of cream, make sure you stop before they are all mixed. Color definition is key.
Freeze cream for 6-10 hours. It can be tempting to remove the ice cream from the freezer prematurely. Wait several hours until it is fully hardened to make sure you have a cold and stable ice cream sandwich.