Clean and wash the vegetables and cut into fine strips. Put them into boiling salted water and cook for 10 minutes. Carefully wash the plaice fillets, sprinkle them with lemon juice, cover each with 1 slice of Parma ham and roll them up.
Fix it with wooden sticks. Bring a large pan of salted water, bay leaves and onion quarters to the boil. Add the plaice rolls and let them simmer at low heat for about 7 minutes. Fill with orange.
Put 2 fillets aside, cut the rest into pieces. Peel and finely dice the shallot. Heat the fat in a pan and fry the diced shallots in it. Add the orange pieces and fry.
Deglaze with the port wine. Add cream and bring to the boil. Add sauce thickener while stirring, bring to the boil again. Season to taste with salt and pepper. Cut lemon balm into strips and fold into the sauce.
Arrange the plaice rolls with the vegetables and sauce on a plate. Garnish with lemon balm and orange wedges.