Brown 2 onions in a little olive oil, then add 400g ground beef. Cook for 5 minutes before stirring in 600g ready-made Bolognese sauce. For the béchamel, melt 125g butter, whisk in 2 tablespoons flour until smooth, then gradually add 500ml milk, stirring constantly until thickened. Layer in an oiled gratin dish: lasagna sheets (store-bought or homemade), Bolognese, sheets, béchamel—repeating until ingredients are gone, ending with béchamel. Top with grated cheese and bake at 180°C for 45 minutes.
Slice 2 zucchinis into rounds and sauté for 10 minutes until tender. Mix with 600g tomato sauce (ready-made or homemade). In an oiled gratin dish, layer lasagna sheets, zucchini-tomato mix, and mozzarella slices. Repeat until ingredients run out, finishing with mozzarella. Bake for 45 minutes and serve hot.
Sauté 500g frozen spinach with 1 tbsp olive oil and 1 chopped shallot, then drain thoroughly. Prepare béchamel (as above) and mix most with the spinach, reserving some. Cube 300g fresh salmon. In an oiled gratin dish, layer lasagna sheets, spinach mixture, and salmon cubes. Repeat, topping with reserved béchamel and Parmesan. Bake for 45 minutes.
