Combine the heavy cream, whole milk, half the sugar (6 tablespoons), the vanilla bean seeds, and the empty vanilla bean pod in a medium heavy-bottomed saucepan over medium heat. Warm the mixture, stirring occasionally, until it just begins to steam and small bubbles form around the edges — do not boil. Remove from heat.

In a large bowl, whisk together the egg yolks and remaining sugar (6 tablespoons) until the mixture is pale, thick, and ribbons off the whisk — about 2 minutes.

Temper the eggs: slowly ladle the hot cream mixture into the yolk mixture one ladle at a time, whisking constantly after each addition. This raises the temperature of the eggs gradually without scrambling them. Continue until about half the cream is incorporated, then pour the egg mixture back into the saucepan with the remaining cream.

Return the saucepan to medium-low heat. Cook, stirring constantly with a wooden spoon or heat-safe spatula, until the custard thickens enough to coat the back of the spoon and reads 170–175°F on an instant-read thermometer, about 5–8 minutes. Do not let it boil.

Remove from heat. Fish out and discard the vanilla bean pod. Stir in the vanilla extract and sea salt. Pour the custard through a fine-mesh strainer into a clean bowl to remove any cooked egg bits.

Place the bowl of custard over an ice bath (a larger bowl filled with ice and cold water) and stir until cooled to room temperature, about 10 minutes. Cover with plastic wrap pressed directly against the surface and refrigerate for at least 4 hours, or overnight. The custard must be completely cold before churning.

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

Transfer the churned ice cream to a freezer-safe airtight container. Press a sheet of plastic wrap directly against the surface to prevent ice crystals. Freeze for at least 2–4 hours until firm and scoopable.

Before serving, let the ice cream sit at room temperature for 5 minutes for easier scooping. Serve in bowls or cones and enjoy immediately.