Step 1

Remove all but the bottom rack from the oven and heat the oven to 300ºF.

Step 2

Place 3 large egg yolks, 1 large egg, 1/3 cup granulated sugar, and 1/8 teaspoon kosher salt in a medium bowl and whisk until combined.

Step 3

If using a vanilla bean, split 1/2 vanilla bean lengthwise down the middle with a paring knife, then scrape the seeds out into a small saucepan and add the bean. (If using vanilla extract, reserve for the end of this step.) Add 1 1/2 cups heavy cream and 1 cup whole milk. Heat over medium-high heat until simmering, 5 to 7 minutes. Turn off the heat and discard the vanilla bean if needed. If using vanilla extract, add 2 teaspoons to the hot cream mixture now.

Step 4

While continuously whisking the egg and sugar mixture, carefully and slowly pour in a little of the hot cream to temper the eggs. (You want to bring the eggs up to temperature without scrambling them.) Whisk in the remaining hot cream in a steady stream until well-combined, about 1 minute. Use a large spoon to scrape off and discard the foam from the top. If the bowl does not have a pouring lip, transfer the custard to a large liquid measuring cup or pitcher to make pouring easier. You should have about 24 to 28 ounces custard total.

Step 5

Place 2/3 cup granulated sugar and 1/3 cup water in a completely dry and clean small saucepan. Cook over medium heat undisturbed until it reaches a light amber color, 12 to 15 minutes. Meanwhile, bring 4 cups water to a boil, and arrange 6 (4-ounce) or 4 (6-ounce) ramekins in a 9x13-inch baking dish or roasting pan.

Step 6

Once the caramel is light amber, turn off the heat and swirl the caramel around in the pan to reduce the bubbles. Then, working quickly, pour the caramel into the ramekins and swirl to evenly coat the bottoms. The caramel will harden fast.

Step 7

Fill each ramekin with the custard up to the raised line right below the lip, or about 1/2-inch from the top. Carefully place the baking dish on the bottom rack of the oven. Pour enough boiling water into the baking dish, being careful not to splash any onto the custards, to reach halfway up the sides of the ramekins. Cover the baking dish with aluminum foil.

Step 8

Bake until the custards are nearly set but still jiggle like jello, 40 to 45 minutes for 4-ounce ramekins, or 45 to 50 minutes for 6-ounce ramekins. (If they ripple like water, they need more time.)

Step 9

Remove the baking dish from the oven and uncover. Let the custards cool in the water until room temperature, about 45 minutes. Individually wrap each ramekin with plastic wrap, then refrigerate until completely chilled, at least 4 hours or up to overnight.

Step 10

When ready to serve, run a small thin knife around each crème caramel so they release easily. Invert a small plate over the ramekin, then flip both at the same time to unmold the crème caramel onto the plate; let the caramel drip down the edges. (If the crème caramels do not unmold easily, dip the bottoms of the ramekin in hot water for a few seconds to help release the sides.)