Tips: You can use either whole cardamom pods or the peppercorn-size seeds for this recipe. Crush or bruise the seeds with the side of a chef's knife or a heavy-bottomed pan to help release the flavor. If necessary, substitute 1/2 teaspoon ground cardamom; the flavor will be fine, but the texture will be a little less silky. Almost any semisweet or bittersweet chocolate will work in this recipe, although if you choose an extra-bittersweet one with more than a 65% cacao content, reduce the chocolate to 4 ounces and increase the sugar to 1/4 cup.
Position a rack in lower third of oven; preheat to 325°F. Lay a double thickness of paper towels in a baking pan large enough to comfortably hold eight 4- to 6-ounce heatproof custard cups or ramekins. Set the cups in the pan (the paper towels will keep them in place).
Heat cream, cardamom, cloves and ginger in a medium saucepan over medium-high heat until the mixture just comes to a full boil. Remove from the heat and let stand for 15 minutes. Place chocolate in a 4-cup glass measure. Return the cream to medium-high heat and reheat to boiling. Immediately pour through a very fine sieve set over the chocolate, pressing down on the spices to extract as much flavor as possible; don't stir the chocolate. Let stand for 3 minutes, then gently stir until the chocolate completely melts and the mixture is well blended and smooth. (If the chocolate is not completely melted, microwave it for 20 to 30 seconds on High, then stir.)
Wipe out the saucepan, add milk and sugar, and heat just to boiling, stirring until the sugar dissolves. In a slow, thin stream, gradually stir about two-thirds of the boiling milk into the chocolate. If the mixture looks separated at any point, stop adding milk and stir the chocolate until it is smooth again before continuing.
Whisk egg, egg yolks and vanilla in a small bowl until well blended. While constantly whisking the egg mixture, add the remaining milk in a slow, thin stream. Strain the egg-milk mixture through a fine sieve into the chocolate mixture; stir well to combine. Evenly divide among the custard cups, about 1/4 cup each.
Place the pan on the low oven rack. Add enough very hot tap water to come 3/4 inch up the sides of the cups. Bake until the tops appear barely set when the cups are jiggled, 16 to 20 minutes; don't tap the tops as this will mar the surface.
Transfer the cups to a wire rack. Let cool thoroughly, about 1 hour. Cover with plastic and refrigerate until chilled, at least 3 hours and up to 3 days. Let warm up just slightly before serving. Garnish with a dollop of whipped cream and a small piece of crystallized ginger (if desired).