Preheat an oven to 160 degrees/gas 3.

Start by topping and tailing the leeks and then cutting them in half lengthways down the middle, so they open up, like you would if butterflying a leg of lamb.

Using a sharp knife, cut the leeks into long spaghetti-like strips, about one centimetre wide. Wash the leeks thoroughly, before blanching for two minutes in boiling water. Drain in a colander and refresh under cold running water until cool, then dry with kitchen paper or a clean tea towel. Toss the strips in the olive oil and season well.

Saute the bacon or pancetta in a big saucepan till it is crisp, then drain it on kitchen paper and set aside. In the same saucepan, sweat the chopped onion in the remaining fat, then add the wine and reduce till the wine is cooked off.

The next bit comes together quite quickly, so make sure you’re ready to go. Add the beaten egg, bacon and 100g of the Parmesan, as well as the 200ml of water, to the onion mixture and cook for about one minute, until it is heated through. Taste, and adjust the seasoning.

Place the leek ‘spaghetti’ in a large gratin dish, pour the sauce over it and sprinkle over the remaining Parmesan. Bake for 20-25 minutes, before giving it a final five-minute blast under a hot grill.