Dice the 2 carrots, 1 leek, 2 onions, and roughly 1/4 of a celery or parsley root into small pieces.
Bring lightly salted water to a boil over medium-high heat in a large pot. Add the diced vegetables and 10 peppercorns. Simmer over medium heat for 5 minutes.
Add the 200 ml white wine and the cleaned, closed mussels to the pot. Simmer over medium-high heat for 5 minutes until the mussel shells open.
Lift the mussels out with a slotted spoon and discard any that remain closed. Serve with 4 small baguettes or black bread slices and butter.