Heat the Combi-steam oven in the 100% Humidity + 212° F mode or bring a pan of water to a boil to blanch the tomatoes. Prepare an ice bath in a large bowl.
With a paring knife, score the top of each tomato with a shallow x, place the tomatoes in the perforated oven pan and steam for 1 minute or blanch in boiling water for 5 seconds to loosen the skin. Cold shock the tomatoes in the ice bath, then remove and peel the tomatoes when cooled.
Place the prepared tomato water in a saucepan and bring to a gentle simmer, level 4 Induction or level 4 Gas cooktops. Add the sugar and whisk to dissolve. Remove from the heat, add the vinegar, salt, lemongrass and lime leaf and set aside to cool and infuse.
When the liquid has cooled, strain out the solids through a fine mesh strainer, add the peeled tomatoes, refrigerate and marinate for a day prior to using.