1. Wash the blue mussels thoroughly under cold, running water. Brush them as often as necessary to remove sand and calcium residues. Pull the beards off with your fingers. Discard any open mussels that do not close when you tap on one of the shells. These may be spoiled. Shake the mussels in a sieve, rinse again thoroughly and drain well.
2. Peel and finely chop the onion and garlic. Trim and peel the carrots, parsley root and celery and cut into pieces approx. 1 cm in size. Wash the lemon in hot water, dry it, grate the peel finely and squeeze the juice.
3. Heat the olive oil in a pot. Sautèe the onions and garlic until clear. Add the vegetable pieces and sweat for 4-5 minutes, stirring continuously. Pour in the white wine and lemon juice, sprinkle herbs on top and season all the ingredients with salt and pepper.
4. Arrange the mussels in the universal pan. Pour the vegetable and wine mixture along with the lemon peel over the mussels. Cook as indicated.
5. After 6 minutes' cooking time, mix the mussels once with a large spatula or briefly remove the universal pan and shake it. Then finish cooking as per setting procedure.