Wash the basil, shake dry, pluck the leaves from the stalks and chop finely, except for something to garnish. Finely puree the tomatoes and stir in the basil. Season to taste with pepper
Peel and wash the Jerusalem artichoke and potatoes and, depending on their size, possibly halve them. Cook in boiling salted water for about 20 minutes. In the meantime, wash the fish and pat dry. Cut the ham slices in half lengthwise and spread 1 tsp of tomato paste on each. Cover with 1 fish fillet each, roll up and pin with wooden skewers
Place the rolls on an oiled baking tray and cook in a preheated oven (electric cooker: 200 °C/ convection oven: 175 °C/ gas: see manufacturer) for approx. 6 minutes. Bring milk and butter to the boil. Drain the Jerusalem artichoke, add milk and butter and mash to a fine puree. Season to taste with salt and nutmeg. Serve the puree, remaining tomato paste and fish rolls. Garnish with basil