1. Preheat oven to 325 degrees. Bring a kettle of water to a boil. In a medium saucepan, bring half-and-half and vanilla just to a boil. Remove from heat.

2. Place egg yolks, sugar, and salt in a medium bowl. Beat until light, then whisk in chocolate. Whisking constantly, gradually add hot half-and-half mixture. Skim any foam from surface.

3. Divide mixture among four (6-ounce) custard cups, and place in a baking dish just large enough to hold them. Place in oven, and pour enough boiling water in dish to come halfway up sides of cups. Drape a sheet of aluminum foil over top of baking dish (do not seal).

4. Bake custards until just set but still slightly wobbly, 40 to 45 minutes. Remove cups from dish; refrigerate until chilled, at least 2 hours.