Brew the espresso – make it strong!
Melt the chocolate in the top of a double boiler or in a large stainless steel mixing bowl (or any heat proof mixing bowover simmering water until the temperature is that of a warm bath, but nowhere near boiling.
While the chocolate is melting, thoroughly butter the insides of the ramekins all the way to the top. Then coat the sides with granulated sugar by pouring in a couple tablespoons of sugar, and rotating the ramekin in your hand. The un-broken butter-sugar coating is essential to the even, columnar rising of your soufflé.
In a clean, dry mixing bowl, copper or otherwise, whip the egg whites until frothy. Add the powdered sugar and beat until they hold a soft peak – but not until hard. A softer consistency folds easier and rises better, so do not over-beat.
After beating the egg whites, beat the yolks into the melted chocolate. While continuing to stir, add the hot espresso.
Immediately fold the whites into the chocolate – gently but thoroughly.
Fill the ramekins with the batter just to the top and bake 8-9 minutes. Sprinkle with powdered sugar and serve immediately, with a little side of whipped cream if you prefer.