Place cream in a bowl and chill until very cold, about 15 minutes. Fill 4 heatproof glasses (6 to 8 oz. each) with boiling water.
In a small saucepan over high heat, bring 3/4 cup water to a boil. Reduce heat to low and whisk in chopped chocolate until smoothly blended. Add 1 tbsp. sugar. Stir over medium-low heat until mixture thickens slightly and coats spoon in a thin layer, 3 to 5 minutes. Cover and keep hot.
Whip cream with 1 tbsp. sugar until thick, but before peaks form (cream should still be pourable). Mix remaining 1/2 tbsp. sugar with hot espresso.
Drain water from glasses. Pour one-quarter of hot chocolate into a glass. Hold a spoon, concave side down, at about a 45° angle so tip of spoon touches inside of glass, slightly above chocolate. Very slowly, pour one-quarter of espresso over back of spoon. Repeat for each glass. Spoon thick cream onto espresso, dividing evenly between glasses. Sift a bit of cocoa over cream if you like. Serve immediately.
Note: Nutritional analysis is per serving.