1. Preheat oven to 350 degree F.
2. Whisk together egg yolks, sugar, and salt in a large bowl until smooth.
3. Bring milk and 3/4 cup cream just to a simmer in a medium heavy saucepan. Remove pan from heat and whisk in chocolate, coffee, and vanilla until smooth. Slowly stir one-third of chocolate mixture into egg mixture until smooth. Stir remaining chocolate mixture into eggs (without creating air bubbles) until smooth.
4. Pour custard through a fine-mesh sieve into a measuring cup. Pour about 1/3 cup each into small (4 ounces) heat-proof custard cups. Tap bottom of each cup on counter to eliminate any remaining air bubbles and place in a shallow roasting or baking pan just large enough to hold cups. Put pan in oven and fill with enough boiling water to reach halfway up sides of cups and cover roasting pan tightly with foil (being careful not to get water in custard cups). Bake in middle of oven until sides are set but centers tremble slightly, 30 to 35 minutes.
5. Remove pan from oven, discarding foil, and carefully transfer cups with a spatula or metal tongs to a rack to cool to room temperature. Chill until cold, about 3 hours.
6. Serve topped with whipped cream and a chocolate-covered espresso bean.