2 cups heavy cream
1 cup half-and-half
1 vanilla bean, split lengthwise, scraped, and seeds reserved
1 cup granulated sugar
1/4 cup water
6 large egg yolks
1 teaspoon kosher salt
1. Prepare an ice water bath by filling a bowl halfway with ice and water; set aside. Combine cream, half-and-half, and vanilla seeds in a large bowl and set aside.
2. Combine sugar and water in a large saucepan and stir until mixture resembles wet sand. Place over medium-high heat and bring to a boil. Let boil until mixture turns dark amber in color and smells toasted, about 5 to 7 minutes. Immediately remove from heat and slowly add cream mixture, whisking until evenly incorporated. Return the saucepan to the stove and place over medium-low heat to keep warm.
3. Meanwhile, whisk egg yolks in a large bowl until pale yellow, about 5 minutes. Whisking constantly, slowly pour about 1 cup of the caramel sauce into the eggs. Pour the egg mixture back into the saucepan with the remaining caramel sauce, stir in salt, and cook over low heat, stirring constantly until it is as viscous as melted ice cream and coats the back of a spoon, about 5 minutes. (When you draw your finger across the spoon, it should make a mark through the custard, which should not run back in on itself.)
4. Remove from heat and strain through a fine mesh strainer into a large heatproof bowl. Place the bowl over the ice water bath to chill, about 10 to 15 minutes, stirring occasionally.
5. Once the ice cream base is cold, cover and place in the refrigerator to chill completely, at least 3 hours or overnight. Once it’s chilled, freeze in an ice cream maker according to the manufacturer’s instructions. The ice cream will keep in the freezer for 1 week.