Adapted from The Last Course via Smitten Kitchen

Ingredients
2 cups heavy cream
1 1/4 cups sugar
6 to 12 large egg yolks (I used 6)
2 cups buttermilk
pinch of salt
1/2 a vanilla bean, or 1 teaspoon good-quality vanilla extract

Directions

Bring the cream and 1 cup of the sugar to a simmer in a heavy saucepan over medium heat (if you’re using the vanilla bean, scrape the seeds into the cream while it heats as well.)

In a separate bowl, whisk together the egg  yolks and the remaining 1/4 cup of sugar.

After the cream comes to a simmer, turn off the heat and dribble a small amount into the egg yolks, whisking them constantly, to temper. Continue slowly adding the hot cream mixture to the egg mixture, whisking all the while. Once everything is incorporated, return the mixture to the saucepan where you heated the cream.

Cook over medium-low heat, stirring continuously, until it thickens enough to coat the back of a spoon. Strain into a bowl and mix in the 2 cups of buttermilk (and the vanilla extract if you are using that instead of the vanilla bean.) Cool this mixture completely, then freeze in your ice cream maker according to the manufacturer’s directions.

Makes about 2 quarts.