Preheat the oven to 325°F.
Boil 5 cups of water to use later in the water bath.
Add heavy cream and salt to a medium saucepan. Heat over medium heat until simmering (do not let it boil!), remove from heat, and stir in vanilla extract. Set aside to cool for 10 minutes.
Meanwhile, place either (8) 4-ounce ramekins, (6) 5-ounce ramekins, or (5) 6-ounce ramekins in a roasting pan or two smaller baking pans and set aside.
Add the egg yolks and 1/2 cup sugar to a mixing bowl. Beat on medium speed for 2 minutes until the egg yolks are pale, fluffy, and thicken.
Using a hand whisk, constantly whisk while slowly drizzling about 1/4 cup warmed heavy cream into the egg mixture. Once completely incorporated, repeat with another 1/4 cup warm cream. When combined, slowly whisk in the remaining cream, constantly whisking. Skim off the foam.
If you notice that the custard is not smooth after adding the cream, you will want to strain it. Place a fine-mesh sieve over a large liquid measuring cup or pitcher to do this.
Evenly divide the custard between the ramekins. Transfer the boiling water to a liquid measuring cup or pitcher.
Transfer the roasting pan with custard to the middle oven rack, and immediately pour the hot water about 3/4 up the sides of the ramekins. (Place the spout on the corner of the roasting pan and slowly pour so water does not splatter onto the custard.)
Bake at 325°F for 25-45 minutes or until the center reaches 170°F. The custard should be barely set, not liquid, but still jiggly. The baking time will depend on the depth of the ramekins; shallow 1-inch ramekins (5-6 ounces) will take closer to 25 minutes, and deep 2-inch ramekins (4 ounces) will take closer to 45 minutes.
Move the custards to a cooling rack and let cool to room temperature (1-2 hours). Cover custards with plastic wrap and refrigerate for 4 hours up to 3 days before adding the sugar topping.