These Italian custards are thickened with gelatin rather than eggs, so they are easier to make than most custards.
In a small bowl, sprinkle gelatin over 1/4 cup cold water, let soften 5 minutes.
Meanwhile, in a medium saucepan, bring cream to a boil over high heat. Reduce heat to low; whisk in sugar and espresso powder until dissolved, about 1 minutes. Whisk in chocolate until melted (be careful not to let it burn), about 2 minutes. Remove from heat.
Whisk softened gelatin into cream mixture until gelatin has dissolved about 1 minute. Stir in milk and salt. Strain into a large liquid measuring cup (for easy pouring). Divide evenly among six 6-ounce coffee cups or custard cups. Refrigerate until set, at least 3 hours.
For a sweeter flavor, use semisweet chocolate.