Rinse the artichokes thoroughly. Fill a large mixing bowl with cold water and squeeze the juice of half a lemon into it. With a large knife, cut off the stem flush with the base of each artichoke. Pull off and discard any small or discolored leaves around the base. Remove one or two rows of leaves by bending outward and down so that the top part snaps off of the leafs fleshy base. Place the artichoke on its side on the cutting board and, with a heavy sharp knife, cut off about 1 1/2 inches from the top. With kitchen scissors, trim off the pointy ends of all the remaining leaves. Halve the artichokes lengthwise and, using a paring knife or a teaspoon, dig out and discard the fuzzy chokes. When each artichoke has been trimmed and halved, drop them into the cold water and continue trimming.

In a very large nonreactive sauce pan, bring the water to a boil and add 1 tablespoon of the salt and the juice of the remaining lemon half. Drop the artichokes into the water and cook them for about 10 to 20 minutes, or until just barely tender (cooking time will depend on the size of the artichoke). Remove the artichokes and drain cut side down in a colander.

In a heavy casserole, heat the olive oil over medium heat. Add the whole garlic cloves and saute for a few seconds, without letting it brown. Add the onion rings, carrots, serrano, bay leaves, peppercorns, oregano, nutmeg, and remaining 1/2 tablespoon salt. Saute the mixture for 2 minutes, stirring occasionally. Add the artichokes, cook for 1 minute more, and add the vinegar and the white wine. Stir together and increase the heat so that the mixture comes to a boil. Lower the heat and simmer, stirring occasionally for 5 minutes. Remove from the heat and set aside in the pan to cool to room temperature. Discard the bay leaves. If desired, the escabeche could be refrigerated for up to 1 week, very tightly covered. Garnish with sprigs of oregano when serving.