Preheat the oven to 400 degrees F.
Butter and dust 6 (1-cup) souffle dishes with about 2 tablespoons of the sugar. Keep in the refrigerator until needed.
Melt the chocolate in a large glass bowl in the microwave, 30 seconds at a time, stirring gently until it is all melted (it takes about 2 minutes total).
While the chocolate is melting, place all 7 egg whites in a stand mixer and whip them with the wire whip attachment until they form soft peaks. Add the lemon juice and the remaining 2 tablespoons sugar and continue to whip the whites until they are stiff but still very shiny.
Take the chocolate out of the microwave and stir in the egg yolks and the liqueur with a spatula.
Stir a quarter of the egg whites into the chocolate mixture to lighten the mix, then gently fold in the remaining whites.
Place the molds on a baking sheet and fill them with the souffle mixture. Run your thumb around the inside edge of each dish so that the souffles will form a hat when they rise. Bake for 8 to 10 minutes, or until the edges are set but the middle is still just a little soft.
Remove from the oven and carefully set the cups on napkin-lined dessert plates. Dust the tops with powdered sugar, if desired, and spoon a dollop of whipped cream into the center of each souffle. Serve immediately.