8 ounces bittersweet (good quality, not unsweetened) chocolate
2 tablespoon unsalted butter
1/4 cup water
1 to 2 tablespoon liqueur*, OPTIONAL, such as Grand Marnier, rum, Chambord, Amaretto
5 eggs, separated
1/4 teaspoon cream of tarter** (use only if not using a copper bowl to whip whites)
Melt chocolate, butter and water into a small saucepan over low heat.
Off the heat stir in the yolks to warmed chocolate.(Do not boil the chocolate) Stir in the liqueur.
Using a copper bowl whisk the whites until they form stiff peaks. With a flat spatula fold 1/2 cup of the whites into the chocolate mixture. Fold in the remaining whites.
Carefully , without deflating the whites, fill, using a spoon, individual ramekins or a 1-1/2 quart bowl. Allow the mousse to set for at least 4 hours.
* Liqueur Every liqueur has a different strength in taste. Add just enough liqueur to bring flavor into the chocolate but not to overwhelm it.
** Cream of tarter is used to stabilize , or give strength to egg whites. Whites are naturally stabilized in copper. Do not use cream of tarter if using copper as the mixture could become toxic.