2 cloves garlic, minced1 tbsp plain flour400 ml pouring cream1.3 kg potatoes, such as desiree, royal blue or Nicola, peeled280 gm butter, coarsely chopped2 leeks, thinly sliced4 sprigs thyme2 fresh bay leaves125 ml (½ cup) dry white wine60 ml (¼ cup) white-wine vinegar 6 pieces (180gm each)mulloway, skin onTo serve:steamed Roman beans
For the gratin, combine garlic in a large bowl with salt and pepper, flour and cream. Finely slice potatoes using a mandolin, add potato to cream mixture and spoon into a 1.5-litre capacity ovenproof dish. Cover with foil, bake at 150C for 1-1½ hours or until potatoes are tender.
For the sauce, melt 30gm butter in a saucepan, add leeks, thyme and bay leaves and sweat for 15 minutes over a medium heat, stirring continuously until soft. Deglaze with white wine and white-wine vinegar. Cook on high heat for 4 minutes or until reduced to a syrup. Remove bay and thyme, purée leeks. Whisk remaining butter, a piece at a time, taking special care not to split the sauce, adjust seasoning.
Cook fish in a hot frying pan which has been lightly oiled, skin-side first, for 4-5 minutes, turn and cook for 2 minutes or until just cooked. Serve with potato gratin, beans and leek sauce.