How to Make It
In a large pot, cover the turkey, onion and garlic with the stock and 3 quarts of water; bring to a boil over high heat. Add a generous pinch of salt and simmer over moderately low heat until the turkey is very tender, about 2 hours and 30 minutes.
Meanwhile, in a large cast-iron skillet, toast the pepitas in the olive oil over moderately high heat until golden, about 3 minutes. Transfer to a small bowl. Add the tomatillos and chiles to the skillet cut side down and cook over high heat until charred on the bottom, about 5 minutes. Transfer to the bowl with the pepitas.
Using tongs, transfer the turkey to a plate; let cool. Discard the skin and bones, then shred the meat. Using a slotted spoon, transfer the onion and garlic to a blender. Add the charred tomatillos, chiles and pepitas along with the 1 cup of cilantro, the epazote (if using), oregano, cumin, crushed red pepper and 2 cups of the turkey broth and puree until the salsa verde is smooth.
Stir the salsa verde into the broth in the pot and season generously with salt. Stir in the turkey and hominy and cook over moderate heat until hot, 5 minutes. Serve the posole with avocado, radishes, crema, lime wedges, oregano and cilantro.