1 C sugar
1¼ C heavy cream
½ tsp kosher or sea salt
½ tsp vanilla
2 C half & half
¼ C brown sugar
Heat sugar in a dry skillet over medium heat (slowly), stirring frequently until sugar starts to melt. Continue stirring and/or swirling the skillet so sugar melts evenly into a dark amber color. (You don't want to burn the sugar!)
Add cream to sugar (watch out, it spatters a bit!) and continue stirring over medium heat until sugar melts again and the two are smoothly blended. Remove from heat. Stir in vanilla and salt. Transfer to a bowl (if desired) and cool to room temperature.
While it's cooling... Whisk eggs in a medium bowl and set aside. Combine brown sugar and half & half in a heavy saucepan and bring just to a boil. Temper the eggs by pouring half of the half & half mixture into the bowl of whisked eggs, whisking constantly; return this mixture to the saucepan and cook over medium heat, stirring constantly until custard coats the back of a spoon (about 170°); do not boil. Pour custard through a fine mesh sieve, then add cooled caramel.
Chill custard at least 4 hours, until very cold. Process in an ice cream maker according to manufacturer's instructions, then transfer to an airtight container to freeze to desired consistency.