Wash and cube potatoes, peeling only if the skin is aging. Boil in a pot with enough broth or water to keep from going dry before potatoes become tender. Add chopped onion and a bay leaf while cooking. Meanwhile, slice cabbage fine and sauté in butter, salt and pepper. When cabbage is al dente, mash the potatoes and stir cabbage into the mixture, along with cream and grated truffle. When serving, make a small well in the top of your heap of colcannon and place a generous pat of butter inside, adding a last grating of truffle and a fine mincing of parsley or chives.