Makes about 1 1/4 quarts, or 8 servings
To get the best ripple in a swirl ice cream, be sure the caramel, or other sauce, is cooled to the right temperature. It should still be soft enough to pour but just slightly thicker than honey so that it falls in a steady stream. It should also be cool enough not to warm up the ice cream.
- Prepare an ice bath. Combine the half-and-half, 1½ cups of the sugar, and the vanilla bean in a heavy nonreactive saucepan over medium heat and bring to a simmer, stirring constantly. Whisk the yolks with the remaining sugar until thick and pale yellow, 2 minutes.
- Temper the egg yolks by gradually adding about one-third of the hot half-and-half mixture, whisking constantly. Pour the tempered mixture back into the saucepan and cook over low heat, stirring constantly, until the custard coats the back of a spoon (about 180°F). Pour the custard through a fine-mesh sieve into a bowl. Set it in the ice bath.
- Scrape the seeds from the vanilla pod into the custard. Stir the custard every few minutes until quite cool.
- Refrigerate the custard for at least 4 hours or up to overnight before freezing in an ice-cream machine according to the manufacturer’s instructions. Just before the ice cream is ready to stop churning, drizzle the caramel sauce into the ice cream with the dasher turning. As soon as the caramel is swirled throughout the ice cream, stop churning immediately. Pack the ice cream in containers and let ripen in the freezer for 3 to 4 hours before serving.