Peel the papery wrapping from the tomatillos and wash them. In a blender, blend the tomatillos, bouillon, garlic, jalapeño and onion. If too thick, add a little water.
Remove excess fat from pork and cut into large chunks. Wash the potatoes and cut them into small pieces.
In a large frying pan, brown the pork well in the olive oil. Reduce heat, add the tomatillo salsa and cover, cooking until pork is tender (about an hour). Add the potatoes about 20-30 minutes before the hour is up. Add water as needed so that meat and potatoes are covered in liquid.