This pasta is a complete revelation. It's been one of the most popular recipes from my Guardian column, so I wanted to include it here. The sauce is magically made from the pasta water and asparagus as the pasta cooks—all in one pan. No fuss, and a killer bowl of pasta.
The key to this recipe is to measure your water carefully and use the right pan: You need a large, shallow sauté pan or a casserole dish large enough to fit the pasta lying down. A large, deep frying pan or wok would work too. Keep tossing the pasta as it cooks to keep it from sticking, as there is less water than you might be used to. Make sure your pasta is a type that cooks in 8 minutes; any longer will need water and more cooking.
I use sorrel here. It's a bright green, lemony, almost juicy leaf that I love. Be sure to add it if you can get your hands on it. If not, use watercress. The flavor will be more peppery than the sprightly lemon tang of sorrel, but both work beautifully.
Fill a kettle with water and boil, and get all your ingredients and equipment together. If you are using spinach or watercress, scrunch it between your hands with a little lemon juice and a pinch of salt.
Put the pasta into a pan. Snap the woody ends off the asparagus and chop the stalks into 1⁄4-inch rounds, leaving the tips intact. Put the tips to one side and throw the rounds into the pan along with the garlic and peas. Grate in the zest of both lemons and add the oil and salt. Add 41⁄2 cups (1 liter) of boiling water, put a lid on the pan and bring to a boil. As soon as it comes to the boil, remove the lid and simmer on a high heat for 8 minutes, using a pair of tongs to turn the pasta every 30 seconds or so as it cooks.
Meanwhile, remove any big stalks from the watercress (if using). Once the pasta has had 8 minutes, take the lid off and stir in the asparagus tips, the sorrel, and the basil or mint. Squeeze in the juice of 1 lemon and simmer for a final 2 minutes.
Once almost all the water has evaporated, take the pan off the heat and leave to sit for a minute or two, so the pasta can absorb most of the remaining water and form a lemony sauce. Tangle into four bowls and top with a little Parmesan.