Preheat oven to 300°F In a small saucepan over medium-low heat, bring cream, milk, espresso powder, and spices to a gentle simmer; cook 10 minutes. Increase heat to medium and bring mixture to a boil, then remove from heat and stir in coffee liquer.
Put chocolate in a heat-proof bowl and pour hot cream over it. Let stand 1 minute, then stir until smooth.
In a separate bowl, whisk together egg yolks and sugar. Slowly drizzle yolk mixture into chocolate mixture, whisking constantly. Pour mixture through a fine mesh sieve into a bowl and let cool at room temperature 15 minutes.
Meanwhile, in a kettle or small pot, bring about 4 cups water to a simmer. Arrange a dish towel in the bottom of a 9-by 13-in. baking pan. Set ramekins on top of towel (this helps keep them in place), then fill each ramekin with custard. Pour simmering water into pan so that it comes halfway up sides of ramekins. Set pan in oven and bake pots de creme until their edges are set but their centers are still wobbly, about 25 minutes; do not overbake. Transfer ramekins to a cooling rack and let cool at room temperature for 30 minutes, then chill in refrigerator until fully set, about 3 hours.