In a heavy large saucepan, place the tomatillos, garlic, onion and 3 cups of water over medium-high heat. Bring to a boil and cook for 15 minutes. Using a slotted spoon, transfer the boiled vegetables into a blender with the cilantro leaves and 1 teaspoon salt. Allow the mixture to cool before blending until smooth. (Reserve the cooking liquid in case you need it to thin out the sauce later.)
Heat the oil in a heavy large saucepan over medium heat. Add the tomatillo salsa and cook until reduced slightly and thickened, about 20 minutes. Season with 1/2 teaspoon sugar if the tomatillos are too tart. Season with some additional salt if needed. Add the cracklings and stir until soft, about 3 minutes. Transfer to a serving bowl, sprinkle with the chopped cilantro and serve with warm corn tortillas.
Cook's Note: Pork cracklings (chicharrones) are sold in every single Hispanic market and some regular supermarkets. In fact, you can find them in most gas stations but they're sold almost as potato chips are sold; in a small bag as a snack. The problem with those is that they are over seasoned and packed with preservatives which won't let them soften properly.