Set a perforated baking sheet or a fine-mesh rack over a rimmed baking sheet. Place tomatoes on perforated baking sheet; sprinkle with sugar and salt. Cover and transfer to refrigerator; let stand overnight to drain.
Transfer tomatoes to a large bowl; set aside. Discard liquid. Place garlic, lemon peel, orange peel, thyme, oregano, and olive oil in a large saucepan over medium-high heat. Cook until heated through. Pour garlic mixture over tomatoes. Cover and transfer to refrigerator; let marinate overnight. At this point, tomatoes and marinade may be stored, covered and refrigerated, until ready to use, up to 2 weeks.
To use tomatoes, remove from marinade and finely chop; reserve marinade for another use.
I, also, spent a lot of time and money on this recipe and the tomatoes were so salty they were really awful. I questioned the 1/2 cup of salt since I thought I remembered Martha lightly sprinkling on the salt
Do NOT use a full 1/2 cup of salt on the tomatoes!!!! The sauce was way too salty, and ruined several days of prep work ruined by following the recipe to a "T." Don't use any more than 1/8 of a cup salt, if that (and I LOVE salt). Nonetheless, the flavors of the sauce were really interesting and I will make it again with this modification.
Also, I think the "curing" stage could probably be skipped altogether if you just strain the tomatoes in a fine mesh colander instead.