Peel onions and cut them into rings. Bring to the boil with red wine, bay leaves, peppercorns, juniper berries and sugar. Leave the maties to soak in the cooled stock for about 2 hours. Roll them up and serve in a tall glass, garnished with dill.
If matie fillets are left over, make a salad of them the next day. Mix the herring, mustard gherkins and beetroot and dress with a vinegar-oil marinade.