01 -
Pulse the peeled and quartered onion briefly in a blender until finely chopped. Use a spatula to scrape down any onion pieces from the blender sides to ensure none is wasted.
02 -
Combine butter, flour, semi-skimmed milk, egg yolk, salt, pepper, and nutmeg in the blender or food processor. Heat gently while stirring frequently until the sauce thickens and bubbles, about 8 minutes, taking care to avoid overcooking or lumps.
03 -
Stir the grated Emmental cheese into the hot sauce and continue stirring for one more minute until fully melted and the sauce turns glossy and smooth.
04 -
Butter a baking or gratin dish liberally to prevent sticking to the first layer.
05 -
Spread a spoonful of the cheese sauce over the base of the dish, then cover evenly with a layer of fresh lasagna sheets, adjusting to fit as needed.
06 -
Spread one quarter of the cheese sauce over the pasta, top with two slices of ham, and a third of the raclette cheese. Repeat this layering process twice more using lasagna sheets, sauce, ham, and raclette cheese until all ingredients are used.
07 -
Top with a final lasagna sheet layer, pour over all remaining sauce ensuring even coverage, then sprinkle generously with the remaining grated Emmental cheese for a golden crust.
08 -
Preheat the oven to 200°C with fan assisted mode. Place the dish in the center rack and bake for 20 minutes until bubbling and the top is beautifully golden brown.