Briefly saute the pork, pumpkin, mushrooms, and leek in butter in a deep medium-sized pot. Add dashi or water. Bring to a boil and add miso (for best consistency, first combine the misos and some broth in a small bowl), then add into the pot. Turn heat down to a high simmer, and cook for about 15 minutes or until all the vegetables can be easily pierced with a fork.