1. Preheat the oven to 200ºC/400ºF/gas 6.
2. Wash, trim and slice 1 leek (see tip) and place in a large shallow ovenproof pan on a medium-low heat with 50g of unsalted butter and a splash of olive oil.
3. Line up 500g of asparagus, trim off the woody ends, then finely slice and add the stems to the pan, reserving the tips for later.
4. Season with sea salt and black pepper, then fry on a medium-low heat for 10 minutes, or until sweet, soft and delicious, stirring regularly and adding a splash of water, if needed.
5. Stir in 50g of plain flour, followed by 2 teaspoons of English mustard, and slowly stir in 800ml of semi-skimmed milk to give you a loose white sauce, then leave to blip away for a few minutes.
6. Stir in 300g each of peas and broad beans and leave to warm through while you rip off, roughly chop and stir in the leaves from ½ a bunch of fresh mint (15g).
7. Smash up the veg for 1 minute with a potato masher, then grate in 70g each of Parmesan and Cheddar and add the asparagus tips.
8. Tear in the pasta sheets, mix up really well to coat and separate, then pull some of the sheets to the top to create a top layer – use the back of a spoon to create some dips and wells.
9. Roughly bash the almonds so you have a mixture of fine and chunky bits, then sprinkle on top and grate over the remaining 10g each of Parmesan and Cheddar cheese. Finish with a drizzle of olive oil and a few scrapings of lemon zest (if using).
10. Bake for 20 to 25 minutes, or until golden and bubbling. Serve topped with a little dollop of pesto (if using), a crunchy green salad and an extra grating of Parmesan, if you like.

For a tasty kitchen shortcut, check out Jamie's Roasted Veg Lasagne from his new frozen range!