Mocha Mousse - bittersweet chocolate

Method

• Coarsely chop chocolate and melt it with coffee in a double boiler over (not in) boiling water, stirring frequently with a wooden spoon to quicken melting and to prevent overheating.
• Remove from over boiling water.
• Let cool to room temperature.
• Meanwhile, whip cream until peaks hold their shape.
• In bowl of an electric mixer, whip egg yolks with 1/4 cup sugar 4 to 5 minutes, until very thick and pale (the consistency should be that of a heavy mayonnaise).
• Beat in vanilla.
• If egg whites are cooler than room temperature, warm by stirring briefly over boiling or hot water.
• In a clean, dry copper bowl, or in bowl of electric mixer, whip egg whites slowly until they start to foam.
• Increase speed to medium.
• When they are an opaque white add remaining 1/2 cup of sugar and salt and beat at medium speed until soft white peaks form.
• Stir egg yolks into chocolate mixture; both should be at room temperature or slightly warmer.
• If the chocolate is not, stir it briefly over boiling or hot water.
• Add Cognac, if desired.
• Fold in whipped cream, working quickly and being careful not to deflate the mixture.
• Fold in half the egg whites, then remaining egg whites.
• Turn mixture out into a serving bowl or ramekins and let cool in refrigerator at least 2 hours, preferably 4, before serving.