Drizzle in the sweetened condensed milk, vanilla extract, and sea salt while continuing to whip.
When the sweetened condensed milk is fully incorporated, move half of the ice cream base mixture to a round metal cake pan or loaf pan. Drizzle half of the caramel sauce over the ice cream base. Sprinkle with half of the toffee bits if using.
Add the remaining ice cream mixture. Drizzle the remaining caramel on top. Add the remaining toffee bits.
Using a chopstick or other thin utensil to swirl the caramel and ice cream base together.
Freeze for at least four hours.
A larger metal pan will freeze more quickly, but any freezer-safe container will work.