In a large bowl, whisk together the condensed milk, extract and salt. Set aside.
Whip the heavy cream with a mixer until stiff peaks form (usually 2-3 minutes.) Fold about 1 cup of the whipped cream into the condensed milk mixture with a rubber spatula.
Fold the lightened mixture into the remaining whipped cream and gently mix until blended.
Pour into a 9x5 loaf pan and freeze (covered) until creamy like soft serve (about 2 hours.) Swirl in any desired mix-ins and return to freezer until solid (about 3 more hours.) See notes below for 3 different flavoring options.
1. Flavoring with mix-ins
Follow instructions in Step 4 for adding mix-ins. Some options are:
1 cup of chopped up cookies
candy bar pieces
nuts or peanut butter
ice cream toppings like caramel sauce.
2. Flavoring with extracts
Instead of vanilla extract in Step 1, use any other flavor desired. Typically, you will use more than you would for vanilla ice cream. Start with 1 Tbsp, then taste the mixture and add more as desired.
3. Flavoring with Jell-O
Add 1 (3.4 oz) package of Jello powder mix to the ingredients in Step 1. Fold in as directed in following steps.