1. Set up your workspace: Preheat your oven to 325°F (163°C). Place six 4-ounce ramekins in a large roasting pan. Fold a kitchen towel and place it in the bottom of the pan beneath the ramekins to prevent them from sliding and to insulate them from direct heat. Bring a kettle of water to a boil and set aside—you’ll need this for the water bath later.
2. Chop the chocolate: Finely chop your dark chocolate into small, uniform pieces (about the size of chocolate chips). This ensures even, quick melting. Place the chopped chocolate in a large heatproof bowl and set aside.

Make the Custard:

3. Heat the dairy: In a medium heavy-bottomed saucepan, combine heavy cream and whole milk. Place over medium heat and heat until the mixture is steaming and small bubbles form around the edges—it should reach about 170-180°F but not boil. Stir occasionally to prevent a skin from forming. This takes about 5-7 minutes. If using espresso powder, add it to the heating cream and whisk to dissolve.
4. Melt the chocolate: As soon as the cream mixture is hot, immediately pour it over the chopped chocolate in the bowl. Let it sit undisturbed for 2 minutes to allow the heat to gently melt the chocolate. After 2 minutes, whisk gently until the chocolate is completely melted and the mixture is smooth and glossy. Start slowly and increase speed as the chocolate melts to avoid creating air bubbles.
5. Whisk the egg mixture: In a separate medium bowl, whisk together the egg yolks and sugar for about 1 minute until the mixture is smooth and slightly lighter in color. You want them well combined but not frothy or full of air bubbles. Add the vanilla extract and salt, and whisk to incorporate.
6. Temper the eggs: This crucial step prevents scrambled eggs. Slowly drizzle about ½ cup of the warm chocolate mixture into the egg yolks while whisking constantly. This gradually raises the temperature of the eggs without cooking them. Once incorporated, slowly pour the tempered egg mixture back into the bowl with the remaining chocolate mixture, whisking constantly until completely smooth and combined.
7. Strain for smoothness: Pour the entire custard mixture through a fine-mesh strainer set over a large measuring cup or bowl with a pour spout. Use a rubber spatula to press the mixture through and scrape the bottom of the strainer. This removes any bits of cooked egg or undissolved chocolate, ensuring perfectly smooth custard. Discard any solids left in the strainer.

Bake the Custards:

8. Fill the ramekins: Carefully pour or ladle the strained chocolate custard into the six prepared ramekins, dividing evenly. Fill each about ¾ full, leaving a little room at the top. If you see any bubbles on the surface, gently pop them with a toothpick or skim them off with a spoon for the smoothest finish.
9. Create the water bath: Place the roasting pan with the filled ramekins on the oven rack (don’t pull the rack all the way out). Carefully pour the hot water from your kettle into the roasting pan, pouring it around the ramekins (not directly on them) until the water comes halfway up the sides of the ramekins. The water bath ensures gentle, even cooking that creates that signature silky texture.
10. Bake: Bake for 25-35 minutes. The custards are done when the edges are set but the centers still jiggle slightly when you gently shake a ramekin—they should wobble like Jell-O, not slosh like liquid. The center should look glossy and slightly loose; it will continue to set as it cools. Don’t overbake, or the custard will be grainy instead of silky. Start checking at 25 minutes.

Cool and Chill:

11. Cool in water bath: Carefully remove the roasting pan from the oven. Let the custards sit in the water bath for 10 minutes, then carefully remove each ramekin using tongs or a towel. Place them on a wire rack and let cool to room temperature, about 1 hour.
12. Chill: Once cooled to room temperature, cover each ramekin tightly with plastic wrap (press it directly on the surface to prevent a skin from forming, or leave a small gap if you prefer). Refrigerate for at least 3 hours or preferably overnight. The custards need this time to fully set and develop their flavors.

Serve:

13. Garnish and enjoy: Remove from the refrigerator 10-15 minutes before serving to take the chill off slightly—this allows the chocolate flavor to be more pronounced. Serve directly in the ramekins, topped with a dollop of whipped cream, chocolate shavings, a few fresh berries, or a tiny pinch of flaky sea salt if desired.