Place the meat and bay leaf in a large casserole, and add just enough water to barely cover it. Turn heat to medium and cook for about 30 minutes with the lid on. The water will start to reduce, and the meat will start browning on its rendered fat. The slow cooking process will produce a tender meat. If after this period of time your meat still looks though, keep cooking and add a little bit more water as needed.
While the meat is cooking, place tomatillos in a saucepan*, cover with water and bring to a boil over high heat. Once it starts boiling, reduce heat to low and simmer until tomatillos are pale green and soft, about 6-8 minute.o
Place the cooked and drained tomatillos in a blender with the pumpkin seeds, sesame seeds, Serrano peppers, garlic, onion, romaine lettuce leaves, Hoja Santa leaves, cilantro leaves, spices, and 1 cup of water or chicken broth. Process until you have a very smooth sauce. Depending on your blender, you may need to work in batches.
By this time, the meat should be starting to brown in the casserole. Pour the sauce over the meat and cook over medium-high heat, stirring frequently to avoid the sauce from sticking to the bottom. Once the sauce starts boiling, reduce the heat to low and simmer gently to allow all the flavors to be absorbed. Add the cubed vegetables and more water as needed.
Keep slowly simmering until the vegetables are cooked, about 8 minutes. Serve warm with a nice portion of rice and corn tortillas to scoop up the mole sauce from the plate.