On a rimmed baking sheet, spread out the tomatillos, onion, chiles and garlic. Slide close up under a hot broiler. When the tomatillos are blackened on one side, 5 or 6 minutes, flip everything over and roast the other side. At this point the tomatillos should be soft through, the onion should be browned, the serranos should have dark blotches and the garlic should be soft. Remove, cool until handleable, then remove the skins from the garlic.
In a blender, process the roasted vegetable to a smooth puree. Film the bottom of very large skillet with oil and set over medium-high. When hot, add the puree all at once and cook, stirring constantly, until as thick as tomato paste.
Stir in the broth and simmer for a few minutes over medium-low for the flavors to come together. Taste and season with salt (the amount will vary widely depending on saltiness of the broth and of the chips.)
Add the epazote and tortilla chips and stir to moisten the chips evenly. Simmer over medium to medium-high just until the chips start to soften, 2 or 3 minutes.
Serve hearty portions drizzled with crema and sprinkled with cheese. Strew with thin-sliced onion and cilantro leaves. While the chilaquiles are delicious as is, feel free to serve them with a sunnyside up egg on top or with coarsely shredded cooked chicken mixed in.