Add sugar to a clean heavy-bottomed saucepan over medium heat.

Cook, gently stirring as needed, until the sugar melts into a deep amber liquid.

Carefully add butter and stir until incorporated.

Slowly add heavy cream while stirring carefully.

Stir in ½ teaspoon fine sea salt.

Remove from heat and transfer caramel to a heat-safe container.

Cool completely.

Chill a mixing bowl and beaters if desired.

Beat 2 cups cold heavy whipping cream until smooth medium peaks form.

In a separate bowl, combine condensed milk, vanilla, and ¼ teaspoon salt.

Stir ⅓ cup completely cooled salted caramel into the condensed milk.

Fold one-third of the whipped cream into the condensed milk mixture.

Gently fold in remaining whipped cream in two additions.

Spread one-third of the ice cream mixture into a 9 × 5-inch loaf pan.

Drizzle with cooled caramel.

Repeat with another layer of ice cream and caramel.

Add remaining ice cream base.

Spoon additional caramel over the surface.

Swirl gently with a butter knife 2–3 times.

Finish with a restrained pinch of flaky sea salt.

Cover tightly.

Freeze at least 6 hours or overnight.

Let stand at room temperature for 5–10 minutes before scooping.