Makes 4 servings
3 1/2 ounces bittersweet chocolate, coarsely chopped (I like scharfenberger)
3 large eggs, separated, at room temperature
1 1/2 teaspoons sugar
Whipped cream or creme fraiche, for serving (optional)
Gently melt the chocolate in a heatproof bowl over a saucepan of simmering water or in a microwave oven using melt function
If necessary, transfer the chocolate to a bowl that can hold all the ingredients. Using a whisk, stir the egg yolks into the chocolate one at a time.
In the bowl of a stand mixer fitted with the whisk attachment or in a bowl with a hand mixer, beat the egg whites until they start to form peaks. Beating all the while, gradually add the sugar. Continue to beat until the whites are shiny and hold medium-firm peaks.
Spoon about one-quarter of the whites over the melted chocolate and stir with the whisk until the mixture is almost smooth. (Stirring in a bit of the whites lightens the chocolate and makes the next step easier.) Spoon the rest of the whites over the chocolate and, using the whisk or a large rubber spatula, very carefully fold in the whites. Be as thorough as you can without overworking the mixture — it's better to have a few white streaks than to beat the bubbles out of the mousse by overmixing (actually, I find the streaks appealing).
Spoon the mousse into a serving bowl or individual bowls or serve it now, or cover it and keep it in the refrigerator until you're ready for dessert.
Top with fresh whipped cream
