1. Chop one onion and one clove of garlic into small pieces. Sauté them in a pot or pan with one tablespoon of olive oil over low heat until the onions become slightly translucent. To bring out the flavors of the onion, start cooking on high heat for 1-2 minutes. Then lower the heat to prevent the onions from burning.
2. Once the onions have taken on a nice golden color, add 800 g of tomato pulp. Season with salt and pepper, and add a generous tablespoon of herbs (of your choice: oregano, basil, thyme). Let it reduce and simmer over low heat for 20 minutes before blending or not, depending on your taste. Unlike fresh tomatoes, canned pulp is rather acidic so make sure to add 2 sugar cubes to sweeten the sauce.
3. While the sauce is simmering, heat a bit of olive oil in a pan to sauté 300 g of ground beef over medium heat for 3-5 minutes. Season with salt and pepper, then mix with the reserved tomato sauce. Make sure to remove excess fat from the meat before mixing it with the tomato sauce, using a slotted spoon.
4. In another pot, melt 70 g of butter, and add the same amount of flour off the heat. Mix until the butter is absorbed. Gradually add 50 cl of milk while stirring to prevent lumps from forming. Put the pot back on low heat and let it thicken for a few minutes. Season with salt, pepper, and a good pinch of nutmeg.
5. Grease a baking dish and spread a layer of béchamel, then a layer of lasagna noodles, followed by meat tomato sauce sprinkled with grated Emmental cheese. Repeat this layering until all the ingredients are used up, ending with a layer of béchamel and sprinkle with grated Parmesan cheese. Cheese lovers can also add slices of mushrooms during assembly.
To finish, preheat the oven to 165°C (thermostat 5/6) and bake for about 45 minutes, until the lasagna is nicely browned. If the lasagna browns too quickly, cover it with aluminum foil.