Preheat oven to 250 degrees. Line two sheet pans with parchment paper. With a Sharpie-type permanent pen, trace six 3-inch circles on each sheet of parchment paper, and flip over in pan (marker side down).
In a standing mixer with the whisk attachment, or using an electric hand mixer on medium-high, beat the egg whites, water and salt until stiff peaks form (a peak on the edge of the beater holds its shape without bending).
With mixer still on medium-high, very slowly add, over the course of 2-3 minutes, 1 cup sugar, cream of tartar, and vinegar.
Add the other 1 1/4 cups of sugar, again very slowly, and vanilla. Beat for 10 minutes on medium speed.
To prepare the piping bag, snip a corner off a large zippered plastic bag or pastry bag. Place a large decorating tip into the corner opening (I use a Wilton 1M). Spoon half of the meringue into the bag and twist the top closed.
Starting in the center of each circle and moving in a circular pattern outward, fill each circle with meringue. Continue piping around the outside edges, forming walls (I usually go around 2 or 3 more times, depending on how tall I want my tortes). Use your finger to smooth out the top where the piping tops. Repeat with remaining meringue until all 12 tortes have been formed.
Place in preheated oven and bake 1 hour, then turn heat off and leave Schaum Tortes in oven for another 30 minutes. Remove and store in an airtight container. Serve with fresh berries and whipped cream and garnish with fresh mint leaves if desired.