We wash the snails with plenty of water and use a knife to clean their shells of any remaining debris. With the tip of the knife, we remove the membrane formed at the opening. In a large pot with warm water, we place the snails and set them aside for a bit. Any that float without having removed their heads are discarded, as they are already dead and unsuitable for consumption. We strain them, return them to the pot, and add a little water, 1 cup of vinegar, and 1 tablespoon of salt. We bring them to a boil, strain them again, and rinse them thoroughly with cold water.

Next, we sauté the onion and add the grated tomatoes, salt, pepper, parsley, sugar, and the boiled snails. We stir for 5 minutes, add a bit of water, and let them simmer for about an hour.