Ingredients

Step by step

1. Preheat the oven to 220°C, fan 200°C, gas 7 and bring a large saucepan of salted water to the boil. Trim the woody ends from the asparagus, add the spears to the saucepan, return to the boil and cook for 1-2 minutes depending on thickness (it should still have quite a bite to it). Drain, refresh in iced water, then drain again once cool. Pat dry and season with a pinch of salt.
2. To make the sauce, melt the butter in a saucepan, stir in the flour and cook for 1-2 minutes. Remove from the heat and gradually stir in the milk. Cook, stirring continuously, on a medium heat until the sauce has thickened. Add the lemon juice, nutmeg and two-thirds of the grated Parmesan. Season to taste.
3. Cut each lasagne sheet into 2 long strips, each about 7.5cm wide. Place in a large bowl and cover with cold water. Leave to soak for 5 minutes. Shake the water from the pasta strips, pat dry and line up on a chopping board.
4. Pour half the cheese sauce into the base of a large baking dish (about 20cm x 30cm). To assemble, place a slice of prosciutto along the length of each lasagne strip. Lay a couple of mozzarella slices on top, followed by 3 thick or 4 thin asparagus spears at the end of each strip then wrap up, repeating to make 8 rolls. Arrange the rolls side by side on the cheese sauce in the baking dish. Pour the remaining sauce down the centre of the dish over the pasta, leaving the asparagus mostly exposed, then sprinkle with the rest of the Parmesan.
5. Bake towards the top of the oven for 20-25 minutes or until golden brown. Leave to stand for 5-10 minutes and serve alongside a green salad, if you wish.