Chocolate mousse

Ingredients:

• 1 cup chilled heavy cream
• 170 g semi-sweet chocolate
• 0.5 tsp instant espresso powder
• 2 tbsp dark rum (or any liqueur) or 1 tbsp water
• 1 large egg
• 2 large egg yolks
• A pinch of salt
• 1/3 cup sugar

Preparation:

1. In a cold bowl, whip the cream until soft peaks form. Set aside.
2. Fill a saucepan about a third full with water and bring to a boil. Chop the chocolate with a chef's knife. Place the chocolate in a medium heatproof bowl and set it over the saucepan with water. Stir occasionally until the chocolate is melted and smooth. Set the chocolate aside. Leave the hot water in the saucepan.
3. In a small bowl, stir the espresso powder into the rum or water until dissolved. Place the egg, yolks, and a pinch of salt in a heatproof bowl. Beat the eggs with a hand mixer until light and fluffy, about 1 minute. Gradually whisk in the sugar, continuing to whisk. Add the coffee mixture.
4. Place the bowl with the eggs over a saucepan of simmering water, and increase the heat to bring the water to a boil. Whisk the egg mixture constantly in a double boiler until it turns pale yellow, is very fluffy, and feels hot to the touch, 3-5 minutes. Remove from the heat and whisk until the mixture cools and thickens. The mixture should fall in ribbons.
5. Stir about a quarter of the egg white foam into the chocolate to lighten it. Using a whisk, quickly fold in the remaining foam (the mixture may become very thick). Fold in the whipped cream, keeping the mixture light. Divide the chocolate mousse into 4-6 serving bowls and refrigerate for at least 2 hours. Serve with cookies, if desired.