For the lasagna

• 1 pack (500g) oven-ready lasagna sheets

For the filling

• 5 bunches spinach, roughly chopped
•  or 6 packs (125g each) baby spinach leaves
•  1 large leek (white part only – 200g), finely chopped
•  3 spring onions (120g), finely chopped
•  ¼ cup (65ml) olive oil
•  500g fresh unsalted ricotta
•  1 pack (300g) cream cheese
•  1 1/3 cups (120g) grated Parmesan
•  2 eggs
•  1/3 teaspoon nutmeg
•  1 teaspoon salt
•  1/3 teaspoon freshly ground black pepper

For the béchamel

• 1.5 litres warm milk
•  125g unsalted butter
•  2/3 cup (120g) all-purpose flour
•  1 teaspoon salt
•  1/3 teaspoon nutmeg