Heat a comal or a large dry frying pan (ideally cast iron) over medium heat. Place the 4 ancho chiles on the hot comal and toast, flipping frequently, until darkened in color and fragrant, be careful not to burn.

Bring a medium saucepan of water to a boil over medium-high heat. Add the toasted chiles and the 1/2 pound tomatillos to the water. Reduce heat to a simmer and simmer until chiles are soft and tomatillos are cooked but not split open, about 10 minutes. Remove from the heat.

Heat the comal once again over medium heat and place the quartered onion, jalapeño, and 2 garlic cloves on the hot comal or frying pan. Char the vegetables until they are blackened on the outside. Remove the garlic as it cooks—it will cook faster than the others. Keep flipping and turning the pieces so they char on all sides. Remove them to a heat proof bowl and let cool slightly,

Heat 2 tablespoons of the vegetable oil in a medium frying pan over medium heat. Add the 1/4 cup pumpkin seeds and 1/4 cup peanuts. Fry in the oil until golden and fragrant, about 2-3 minutes. Add the 2 tablespoons sesame seeds and remove from the heat. Stir frequently as they cool to prevent the sesame seeds from burning.

Place the charred veggies in a blender. Remove the chiles and tomatillos with kitchen tongs and place them in the blender as well. Finally add the toasted nuts and seeds, the 1/2 cup cilantro and the 2 teaspoons kosher salt. Add a ladle of the chile cooking liquid and blend until very smooth.
Heat the remaining 2 tablespoons of the oil in a large pot over medium heat. Once the oil is hot, add the pureed chile mixture and stir—be careful the sauce will spatter. Keep stirring, frying in the oil until the color darkens and it thickens slightly.

Add the 3 cups vegetable broth and bring the sauce to a low simmer. Cook, covered for about 15 minutes or so to let the flavors concentrate. Taste and add more salt if necessary. Sauce can be made up to 5 days in advance or frozen for up to 3 months.