Melt the fat in a pot. Stir in flour and sweat briefly. Add stock and milk while stirring. Bring to the boil, boil for 3-5 minutes and season with salt and pepper. Grate cheese finely, except for about for sprinkling, add to the sauce and melt while stirring
Clean, wash and cut the leek into pieces of about 5 cm. Cook in boiling salted water for about 4 minutes. Cut lime in half, squeeze juice from one half. Cut the remaining half into slices. Wash the salmon, dab dry and season with salt, pepper and lime juice
Put half of the sauce into an oiled ovenproof dish. Layer leek and salmon in the mould. Spread the rest of the sauce on the salmon and sprinkle with cheese. Bake in a preheated oven (electric cooker: 200 °C/ convection oven: 175 °C/ gas: level 3) for approx. 15 minutes. Arrange on plates and garnish with lime wedges