The original recipe calls for brandy, not whiskey, but I never seem to have brandy around. We’re whiskey people. You can use whichever you want.
About the chocolate: the good people at Cook’s Illustrated use Ghirardelli bittersweet (60% cacao) chocolate for this recipe, and I do too. You could use a fancier brand, if you want, but whatever you use, it should contain about 60% cacao. Chocolates with a higher cacao percentage have less sugar and a starchier consistency, and they won’t work well in this recipe.
Also, about serving size: chocolate mousse is, by definition, serious stuff. I am pretty much a total pig about dessert, but I recommend that you offer this in small servings. The recipe makes six to eight servings, and I lean in favor of eight. Especially since I like to serve it with a whack of whipped cream on top.
Combine the chocolate, cocoa powder, espresso powder, water, and whiskey in a medium heatproof bowl. Place over a saucepan filled with 1 inch of gently simmering water, and stir frequently until the chocolate is melted and the mixture is smooth. Remove from the heat.
In another medium bowl, combine the egg yolks, 1 ½ teaspoons sugar, and salt. Whisk until the mixture lightens to a pale yellow color and thickens slightly, about 30 seconds. Pour the melted chocolate mixture into the egg mixture, and whisk until combined. Set aside for about 5 minutes, until just warmer than room temperature.
In the bowl of a stand mixer fitted with the whisk attachment, beat the egg whites on medium-low speed until frothy. Add the remaining 1 ½ teaspoons sugar, increase the mixer speed to medium-high, and beat until soft peaks form when the whisk is lifted. Detach the whisk and bowl from the mixer, and whisk the last few strokes by hand, making sure to scrape up any unbeaten whites from the bottom of the bowl. Using the whisk, stir about ¼ of the beaten egg whites into the chocolate mixture, to lighten it. Then, using a rubber spatula, gently fold in the remaining egg whites until only a few white streaks remain.
In the now-empty mixer bowl, whip the heavy cream at medium speed until it begins to thicken. Increase the speed to high, and whip until soft peaks form when the whisk is lifted. Using a rubber spatula, fold the whipped cream into the mousse until no white streaks remain. Spoon into 6 to 8 individual serving dishes – I like to use teacups – or, if you’re feeling casual, mound it up in a single serving bowl. Cover with plastic wrap, and refrigerate until firm, at least 2 hours and up to 24 hours.
For best texture, let the mousse sit at room temperature for 10 minutes before serving. Serve with very lightly sweetened whipped cream.
Yield: 6 to 8 servings