Place the bone-in, skin-on chicken thighs in a pot and cover with cold water by 1 inch. Bring to a gentle simmer over medium heat and cook until the meat is tender and reaches 165°F, 25–30 minutes. Turn off heat, let rest in the hot liquid 5 minutes, then transfer to a bowl to cool and shred into bite-size pieces. Reserve 1 cup of the cooking liquid if you wish to use it in place of stock.
In a separate pot, combine the tomatillos, serrano chiles, white onion, and garlic. Add water to cover, bring to a simmer, and cook until the tomatillos turn olive-green and are soft, 8–10 minutes. Drain well.
Heat 0.5 cup vegetable oil in a medium skillet over medium heat until shimmering. Working one at a time, fry the corn tortillas 10–15 seconds per side until pliable but not crisp. Drain on paper towels and keep warm under a towel.
Spread a thin layer of hot sauce in a 9×13-inch baking dish or large skillet. Working quickly, dip each tortilla into the sauce to coat, place a line of shredded chicken down the center, roll into a cigar shape, and arrange seam-side down in the dish. Spoon the remaining sauce over the top and warm on low heat or in a 300°F oven until heated through, 3–5 minutes.
Drizzle with Mexican crema, sprinkle with queso fresco, and top with thinly sliced white onion and chopped cilantro. Serve immediately.