Start by blending your tomatillos, serrano chiles, garlic clove, and onion with a pinch of salt until smooth. You can use raw tomatillos for a brighter, tangier salsa or roast them first for a deeper, smokier flavor. I usually go with roasted tomatillos because the extra step is worth the flavor boost. Set this salsa aside while you prep the chicharrón.
In a skillet with a little oil, fry the chicharrón prensado for about 2 minutes to wake up its flavor. Pour in the salsa verde and let everything simmer together for 8 to 10 minutes, stirring occasionally, until the mixture thickens into a rich guiso. This filling is really the heart of the whole dish, so don't rush this simmering step.
While the filling cooks, knead your corn masa with water and a pinch of salt until it turns smooth and pliable, similar to soft playdough. It shouldn't stick to your hands or crack at the edges. If it feels too dry, add water a tablespoon at a time until it's just right.
Divide the masa into small balls, roughly the size of a golf ball, then flatten them into thick discs about half an inch thick. If you want stuffed gorditas, place a spoonful of the chicharrón filling in the center before sealing the edges closed. Don't overfill them or the guiso will leak out while cooking.
Heat your comal or griddle over medium heat and cook the gorditas on both sides until they develop light golden spots and feel firm to the touch. This usually takes a few minutes per side. A properly hot comal is key here, since a lukewarm surface leaves the inside raw.
Once cooked, slice each gordita open with a small knife and spoon in extra chicharrón filling, or serve them open-faced sope-style topped with the guiso, chopped onion, and a drizzle of extra salsa. Either way, serve them warm right away for the best texture.