Chocolate Mousse

Break the dark chocolate into small pieces and place in a heatproof bowl together with the butter. Melt over a double boiler set over barely simmering water, making sure the bowl doesn't touch the water, then stir until smooth.

Separate the yolks from the whites. Let the chocolate-butter mixture cool slightly until warm rather than hot, then quickly whisk in the yolks until smooth.

Whip the egg whites to soft foam, gradually add the sugar and continue beating until you get stiff, glossy peaks.

Fold about a third of the whipped whites into the chocolate base to lighten it. Add the remaining whites in 2 batches, gently folding from bottom to top with a spatula so as not to deflate the foam.

Spoon the mousse into 4 individual ramekins or glasses, cover and refrigerate for at least 4 hours to set.

Serve the mousse well chilled; if desired, let it sit at room temperature for 5 minutes before serving for a softer texture.