4 ounces bittersweet chocolate, cut into small pieces
2 cups heavy cream
1/2 cup milk
5 egg yolks
1/4 cup granulated sugar
Grated chocolate, for garnish
1 tsp. Vanilla extract
1 Tablespoon coffee liquor
1-1 1/2 tsp. instant-espresso powder
Heat the oven to 300°F and arrange a rack in the middle. Bring about 4 cups water to a simmer over medium heat. Arrange 6 (6 ounce) ramekins 1/2 inch apart in a large baking dish; set aside.
Place cream and milk in a small saucepan over medium heat and bring it just to a simmer. Remove from heat, add chocolate, and stir until completely melted, about 3 minutes; set aside. If adding extra flavoring like vanilla or liquor, stir it in now.
Whisk sugar and yolks in a large bowl until thickened and pale in color. Slowly whisk in 1/3 of the chocolate mixture, then add the remainder while constantly stirring.
Place a fine mesh strainer over a large measuring cup or a bowl with a spout, and pour in the custard. Remove the strainer and evenly divide the custard base among the ramekins. Tap each ramekin a few times to break any bubbles that appear on the surface.
Place the baking dish in the oven, and carefully add enough of the simmering water to reach 1 inch up the sides of the ramekins. Cover the dish with aluminum foil and poke several holes in the foil to allow steam to escape. Bake 25 minutes or until the outer 1 inch of each custard is set (the centers will still be slightly jiggly).
Remove the ramekins to a rack and let cool to room temperature, about 1 hour. Serve immediately or cover and refrigerate up to 4 days. If refrigerated, let the pots de crème come to room temperature for 20 minutes before serving.