Step 1 Working with one sprout at a time, remove as many of the outer leaves as you can until you reach those firmly attached to the core. Trim the stem end, freeing more leaves, and repeat until you reach the dense center. Slice the center thin.
Step 2 Warm the olive oil or duck fat in a very large nonreactive saucepan. Add the carrot, celery and onion (together they make the mirepoix) and the pancetta and cook over medium heat for 5 to 8 minutes, without browning the vegetables, until they have softened.
Step 3Add one-half cup water and the Brussels sprouts, sprinkle with the salt and stir well to combine. Cover the pan and cook for 15 to 20 minutes, stirring every so often until the leaves are tender. Season with a little freshly ground pepper, correct for salt and add a dash of vinegar. Serve while the color is still vivid.