Have ready a tray lined with a double thickness of paper toweling. First make the sauce. Put the lime juice and salt into a glass bowl, mix in the rest of the ingredients, and leave for at least 30 minutes to marinate. This should make about 1 cup. Spread 1 tablespoon of the ricotta over half of each tortilla. Fold over and secure with a toothpick. Put oil to a depth of 1/4 inch in a large frying pan and heat. When hot but not smoking, add a few of the tacos and fry, turning once until they are a golden color and quite crisp. Continue with the rest, adding oil if necessary. Drain the tacos well on paper toweling and remove as soon as they are cool enough to handle. With a toothpick, ease them open and insert about 2 tablespoons of the sauce. Serve immediately; they cannot wait. The Art of Mexican Cooking From the collection of Jim Vorheis