To make the salsa: Husk and wash the tomatillos. Put the tomatillos and 3 Serrano chiles and some salt in a pot of water and boil them until tender, about 10 to 15 minutes. Then drain them and put them in the bowl of a food processor. Add the coriander, onion, and garlic. Process until smooth. Heat 1 tablespoon lard in a medium large skillet over medium-high heat. When the lard is hot enough to make a drop of the tomatillo puree sizzle, pour it all in at once. Stir the sauce constantly for 4 to 5 minutes until it gets darker and thicker...thick enough to coat a spoon. Add the chopped tomatillos and cilantro. Season with salt. Mix the shredded chicken with 1/2 cup cooked tomatillo sauce.