Heat oven to 225 degrees F. Slice each tomato lengthwise into 4 equal slices. Spread in single layer on rimmed sheet pans. Sprinkle with sugar and vinegar.
Bake in 225 degree oven 2-1/2 hours, until dried but still pulpy, turning slices over after first hour.
Store in airtight container in refrigerator for one week or freeze for longer storage. Makes 32 tomato slices.
