Step 1

Whip the cream: Whip the heavy whipping cream to soft peaks, then chill.

Step 2

Melt the chocolate: Put the chocolate, cubed butter, and espresso in the top of a double boiler over hot, steamy water (not simmering), stirring frequently until smooth.Remove the chocolate mixture from the heat and let it cool until the chocolate is just warm to the touch. Don't let the chocolate get tool cool or the mixture will seize when the other ingredients are added.

Step 3

Whip the egg whites: Once you've taken the chocolate mixture off the heat and it has started to cool, whip the egg whites until they are foamy and beginning to hold a shape. Sprinkle in the sugar and whip until the egg whites form stiff peaks.

Step 4

Add egg yolks to chocolate: When the chocolate has cooled until it is just warm to the touch, stir in the egg yolks.

Step 5

Add whipped cream and egg whites: Gently stir in about one-third of the whipped cream to thin and loosen the chocolate mixture. Then fold in half the egg whites. Fold in the remaining egg whites. Fold in the remaining whipped cream.

Step 6

Spoon into serving dishes, chill: Spoon or pipe the mousse into a serving dishes. If you wish, layer in fresh raspberries and whipped cream. Chill in the refrigerator for 8 to 24 hours.