In a medium saucepan, combine 1 cup of the heavy cream, the whole milk, half the sugar (6 tablespoons), the scraped vanilla bean seeds, and the vanilla pod. Heat over medium heat, stirring occasionally, until steaming and just beginning to simmer around the edges — do not boil. Remove from heat.

In a medium bowl, whisk together the egg yolks and remaining sugar (6 tablespoons) until the mixture is pale, thick, and falls from the whisk in a ribbon, about 2 minutes.

Temper the eggs: while whisking the yolk mixture constantly, very slowly pour in the hot cream mixture in a thin, steady stream. Go slowly — rushing this step will scramble the eggs. Once about half the hot cream is incorporated, pour the tempered yolk mixture back into the saucepan.

Return the saucepan to medium-low heat. Cook the custard, stirring constantly with a wooden spoon or heatproof spatula and scraping the bottom of the pan, until the custard thickens enough to coat the back of a spoon and registers 170–175°F on an instant-read thermometer, about 6–8 minutes. Do not let it boil.

Remove from heat and strain the custard through a fine-mesh sieve into a large bowl or measuring pitcher to remove the vanilla pod and any cooked egg bits. Stir in the remaining 1 cup of heavy cream, the vanilla extract, and the sea salt. Stir to combine.

Set the bowl over an ice bath and stir occasionally until the custard is cool, about 20 minutes. Alternatively, cover the surface directly with plastic wrap (to prevent a skin from forming) and refrigerate for at least 4 hours or overnight. The base must be thoroughly cold before churning — overnight chilling gives the best results.

Pour the chilled custard into your ice cream maker and churn according to the manufacturer's instructions, typically 20–25 minutes, until the ice cream reaches a thick, soft-serve consistency.

Transfer the churned ice cream to an airtight, freezer-safe container. Press a sheet of plastic wrap directly onto the surface of the ice cream to prevent ice crystals. Seal with the lid and freeze for at least 2–4 hours, or until firm enough to scoop.

To serve, let the ice cream sit at room temperature for 5–8 minutes to soften slightly for easy scooping. Scoop into bowls or cones and enjoy.