Place the meat, onion, carrots, bay leave, garlic, nutmeg and marjoram in a large pot and cover with water and cook for about 1 ½ hours until the meat is tender.
When the seeds are cold or warm, is ground into a fine powders. If you do not have a mill to process the seeds, can be liquefied after the other ingredients together, but then the sauce will have a texture more fat.
While the meat is cooking prepare the Pipian Sauce. In a frying pan greased with a little oil roast the pumpkin seeds over low heat. Stir frequently to prevent burning them and when the seeds start popping, turn off the heat and set aside to cool. When the seeds had cool down, ground in your spice grinder until you obtain a fine powder. If you do not have a spice grinder, the seeds can be process later on in a blender together with the other ingredients for sauce but then final result of the sauce will have a grainy texture. Just process some extra seconds to get a fine sauce.
Meanwhile in a large pot big enough to fit the meat, start roasting the tomatos, serrano peppers, garlic cloves and poblano pepper with 3 tablespoon of vegetable oil. Turn the tomatoes and peppers occasional to roast evenly. When they are well roasted and cook, add salt and about a ¼ cup of the meat broth or water. Then add the grinded seeds. Add more broth or water is needed, do not let it to get dry, the sauce at this stage should be very liquid.
After half an hour if you have a blender, food processor or an immersion blender the kind that can be used inside the pot, blend the ingredients to form a smooth sauce then add the meat. Simmer to finish cooking the sauce.
The Pipian Sauce will be ready when the sauce gets thick and has formed bright green puddles.