Sift powdered sugar and put 1 cup into a large bowl. Mix together HALF the egg white, lemon juice, and mint extract. FOR THIS RECIPE YOU SHOULD USE PASTEURIZED EGG PRODUCT OR DEHYDRATED EGG WHITE BECAUSE THE SWIRLS WILL NOT BE COOKED. (This will probably make your math for the egg whites difficult, but try your best.) Make a hollow in the powdered sugar and pour the mixed wet ingredients in. Stir, then squeeze like dough until smooth. Then into another bowl, sift the cocoa powder. Boil a small amount of water and add 2 tsps of it, plus the vanilla. Stir. Then add the rest of the egg white and stir again. Add 1 cup of powdered sugar. Stir and squeeze. Wrap both pieces in plastic wrap and refrigerate 10 minutes.
Sprinkle a surface with powdered sugar and roll out the white piece to 8 x 6. When finished, roll out the chocolate piece as well, and place it on top of the white piece. Roll the whole thing up like a giant sausage, then chop small pieces with a very sharp knife. Caution: If you over-chill this, it will be very hard to roll out, so chill sparingly.