Remove the base of the leek whites. Cut them in half lengthwise, wash them, and then finely slice them.
Sauté the leeks in 10g of butter with a pinch of salt over medium-high heat for about 15 minutes, stirring regularly.
Wash the zucchinis, trim the ends, cut along the central seeds, and dice them.
Sauté the diced zucchinis in olive oil with a pinch of salt over high heat for 5 minutes.
Check the salmon fillet for bones and remove any with tweezers.
Cut the salmon fillet into small cubes.
In a saucepan, melt 75g of butter. When it sizzles, add the flour all at once and stir with a wooden spoon for 2 minutes.
Gradually add the milk, stirring constantly, until a smooth béchamel sauce forms.
Add the heavy cream, leeks, and zucchinis, mixing until well combined. Season with salt, pepper, and a pinch of nutmeg.
Assemble the lasagna by layering lasagna sheets, salmon cubes, and vegetable béchamel.
Top with grated cheese.
Bake at 180°C for 30 minutes.
Garnish the lasagna with parsley leaves before serving.