Have ready at least 30 pieces of banana leaf about 9 by 8 inches (23 by 20 cm), passed over a flame or burner to soften, and a tamale steamer with water and coins in the bottom.
THE MEAT: Mix the meat with the lime juice and salt and set aside for 30 minutes.
THE SAUCE: Put the 1/2 cup (125 ml) water into a blender, add the garlic, cumin, cloves, peppercorns, and oregano, and blend until smooth. Gradually add the onion and tomatoes and blend again until almost smooth. Separately, drain the guajillos, tear into pieces, and put into a blender with the costeños and about 2/3 cup (164 ml) water. Blend as smooth as possible. Add to the other blended ingredients, pressing through a fine strainer to extract any hard bits of skin. Add salt and mix well.
THE MASA: Beat the lard for about 3 minutes or until thickened and fluffy. Gradually add the salt. Mix the water and baking powder and add.Continue beating for 3 more minutes. Add the masa, a little at a time, beating well after each addition, until all the masa is incorporated. Continue beating for a minute or so more; the dough should be moist and porous but fairly stiff.
Grease your hands, take a ball of the dough about 1-1/2 inches (4 cm) in diameter, and flatten it into a very thin circle in the center of a piece of banana leaf. Put a piece of the meat and a very full tbsp of the sauce onto one side of the dough. Fold the leaf over so that the other side of the masa covers the filling. Fold the 2 sides together and fold back the 2 ends. Continue with the rest of the tamales.
Meanwhile, set the steamer over low heat so that the water is boiling and the coins jiggling around by the time you have assembled all the tamales. Put one layer of the tamales into the steamer, cover, and cook for 8 minutes (so that the bottom layer does not get completely flattened) and place the remaining tamales in overlapping layers into the steamer. Cover with more leaves or a towel and steam for 2 hours. Always keep some water boiling on the side in case you need to replenish the water in the steamer--test in the usual way: the masa should separate from the leaf easily, but make sure that the meat is thoroughly cooked through.