Prepare your oven: Preheat to 300°F (150°C) and position a rack in the lowest part of the oven.

Heat the cream: In a medium saucepan, heat the heavy cream over medium-low heat until it just begins to simmer around the edges (do not boil). If using a vanilla bean, add the split pod and scraped seeds to the cream while heating.

Prepare the egg mixture: In a medium bowl, whisk together the egg yolks, granulated sugar, and salt until the mixture becomes pale yellow and slightly thickened, about 2-3 minutes.

Temper the eggs: Very slowly pour about 1/4 cup of the hot cream into the egg mixture while whisking constantly. This prevents the eggs from scrambling. Gradually add the remaining cream, continuing to whisk.

Strain the custard: Pour the mixture through a fine-mesh strainer into a clean bowl or measuring cup with a spout. Stir in the vanilla extract if using instead of a vanilla bean.

Fill the ramekins: Divide the custard evenly among four 6-ounce ramekins.

Prepare the water bath: Place the ramekins in a large baking dish or roasting pan and carefully pour hot water into the pan until it reaches halfway up the sides of the ramekins.

Bake: Carefully transfer the water bath to the oven and bake for 35-40 minutes, or until the custards are set but still slightly jiggly in the center.

Cool completely: Remove the ramekins from the water bath and allow them to cool to room temperature. Cover with plastic wrap and refrigerate for at least 2 hours or up to 2 days.

Caramelize the sugar topping: When ready to serve, sprinkle about 1-2 teaspoons of granulated sugar evenly over each custard. Using a kitchen torch, melt the sugar until it bubbles and turns a deep amber color. Alternatively, place under a broiler for 1-2 minutes, watching very carefully to prevent burning.

Serve: Allow the caramelized sugar to harden for 1-2 minutes before serving.