For an elegant touch, serve Cognac with this dessert. It will complement the caramel flavors of the burnt-sugar topping.
Place chocolate in a heatproof bowl. Arrange four 4 1/2-inch creme brulee dishes (1 inch deep) on a baking sheet. Freeze.
Meanwhile, whisk together yolks, espresso, granulated sugar, and a pinch of salt until sugar has almost dissolved. Bring cream and milk to a boil in a saucepan; gradually whisk about half into yolk mixture. Return mixture to saucepan; whisk. Cook over medium-low heat, stirring, until mixture is thick and reaches 175 degrees on an instant-read thermometer, about 6 minutes; pour over chocolate, and whisk until chocolate has melted and is smooth. Divide among molds, and freeze until firm but not frozen, 45 to 55 minutes.
Sprinkle 1 tablespoon raw sugar onto each custard; shake off excess. Caramelize tops using a handheld kitchen torch.