For an even deeper flavor, toast the cumin seeds and mustard seeds in a dry pan over medium heat for a few minutes before adding them to the pot. This will enhance their aroma and complexity. If you prefer a smokier flavor, consider adding a chipotle pepper in adobo sauce to the beans during the simmering process. Be sure to remove it before serving! Dried epazote can be difficult to find; if unavailable, substitute with a pinch of anise seeds or a few sprigs of fresh cilantro. Adjust the amount of chili pods to your spice preference. For a milder flavor, remove the seeds and veins from the pasilla pods before adding them to the pot. These beans can be made ahead of time and stored in the refrigerator for up to 3 days. The flavors will meld and deepen over time.