Preheat oven to 200°C / 400°F.
In a pan with olive oil add garlic and sliced leeks. Cook for 5–10 minutes until soft and slightly caramelized. Season with salt and pepper.
In a saucepan melt butter, add flour and cook for 1-2 minutes. Whisk in the milk and cook until smooth, slightly thick but still pourable. Add nutmeg, lemon juice, salt and pepper.
In a baking dish: layer thin layer of béchamel, lasagna sheets, leeks, béchamel, and repeat layers. Finish with béchamel, grated cheese and optional chopped basil.
Bake for 30-40 minutes until golden and bubbling.
Let rest 10 minutes before serving.
