01 -
Place the peeled and quartered onion in a blender. Blend for 2 seconds at speed 5, then scrape down the sides with a spatula.
02 -
Add butter, flour, milk, egg yolk, salt, pepper, and nutmeg to the blender. Cook for 8 minutes at 90°C on speed 4 until smooth and thickened.
03 -
Add 100 grams of grated Emmental cheese to the sauce and cook for an additional minute at 90°C on speed 4 until fully melted.
04 -
Butter a large gratin dish. Spread a thin layer of Mornay sauce on the bottom to prevent sticking.
05 -
Place a layer of lasagna sheets in the dish, trimming as needed. Spread one quarter of the Mornay sauce over the pasta, followed by 2 slices of ham and one third of the sliced raclette cheese.
06 -
Add a second layer of pasta. Top with one third of the remaining sauce, 2 slices of ham, and more raclette cheese. Repeat for a third layer: pasta, half the remaining sauce, 2 slices of ham, and the last of the raclette cheese.
07 -
Finish with a final layer of lasagna sheets. Spread the remaining Mornay sauce on top and sprinkle with 40 grams of grated Emmental cheese.
08 -
Preheat the oven to 200°C. Bake for 20 minutes until the surface is golden brown and bubbling.