Heat a skillet over medium heat, working in batches toast the pepitas until they are slightly toasted and start popping, stirring constantly to keep them from burning, about 2 minutes per batch.
Working in batches, blend the tomatillos, onion, garlic, chicken broth*, chiles, epazote, cilantro, pepitas, and cumin. The sauce will be thick and have a grainy appearance, but make sure that it doesn't feel grainy to the touch and that everything is well blended and almost smooth. This may take several minutes in the blender. I usually blend about half the ingredients for 1 full minute, then add the other half and blend until smooth. *I start with 2 cups of chicken broth and use more if needed to achieve a smooth consistency.
Heat oil in a large pan over medium heat until shimmering, about 2-3 minutes. Add the sauce and bring to a simmer, slowly stirring in one direction only for about 25-30 minutes. The sauce will start to thicken and take on an army green color. You can use additional broth here to adjust the consistency if desired.
The mole should be thick, but still have a liquid consistency (you don't want to cook this down to a paste, it should still be pourable). It will also be aromatic. Taste the sauce after about 25 minutes and adjust for salt and broth as necessary.