Preheat oven to 350° F.

Prepare soufflé cups by coating them lightly with cooking spray, then coating them with sugar. To do this, pour about 1/2 cup sugar into a sprayed up. Holding another cup underneath, rotate the first cup so that all sides are coated with sugar, while the excess sugar spills out to the second cup underneath. Repeat the process until all four cups are evenly coated with sugar. (See photo on left.)

Prepare a "Bain Marie" by placing the cups in a baking dish, then filling the dish 3/4 the way up the sides of the cups, with warm water. Baking the soufflés this way helps them to rise and cook evenly. Set aside the prepared cups.

Beat egg yolk until thick and pale yellow (about 5 minutes). Add 2 T sugar, lime juice, triple sec, flour and zest. Beat well, then set aside.

Beat 5 egg whites until foamy. Add cream of tartar and 3 T sugar (add sugar gradually) and Beat until stiff peaks form.

Stir 1/3 of egg white mixture into yolk mixture in order to lighten it. Gently fold in the remaining egg whites. Spoon mixture into 4 - 3/4 cup soufflé cups and bake for about 10 minutes or until puffed and lightly browned. Sprinkle with confectioner's sugar. Serve immediately.