1. Get out a large pan that comes with a tightly fitting lid, and fill it with 2.5L water from a just-boiled kettle. Clamp on the lid, and bring the water back to the boil on a large burner on your hob. Sit a large colander in the sink, break open your bag of baby spinach leaves with gusto and tip the contents into the waiting colander.
2. Get out a clean tea towel (not a terry toweling or waffle one, just a smooth, thin one) and take it over to the stove. Once the water’s boiling vigorously, add 1tbsp fine salt, which will make the water rise up fizzingly. Wait for it to subside, then give it a good stir and, once the water’s boiling again, add the pasta, and stir with a pasta fork to help it submerge. Once the water has come back to the boil, cook for 2 mins, stirring often to detangle and declump the spaghetti. Once the 2 mins are up, take the pan off the heat – though just to a neighbor burner – cover with your tea towel and clamp on the lid for 8 mins, during which you can prepare your remaining ingredients.
3. Remove the lid and tea towel, give the spaghetti a good old stir, then scoop out 500ml of the starchy pasta cooking liquid with a jug or mug: it’s this that makes the sauce so luxuriously creamy. If you taste a strand of pasta, you should find it’s almost properly cooked, but still has a tiny bit of bite to it.
4. Drain the pasta into the spinach-filled colander – thereby wilting the leaves – and take the pan back to the hob, leaving the colander in the sink for now. Quickly spoon the peanut butter into the warm pan and add about 125ml of the reserved pasta cooking water and stir well. It will look grainy and alarming at first, and when you look at the curdled clumps, you’ll think something’s gone wrong. It hasn’t! Just carry on stirring, adding the minced garlic, dried thyme, chilli flakes, 2tsp lemon juice and ¼ tsp salt, and you will swiftly see a pale, herb-flecked emulsion come into being. Slowly stir in another 125ml of the pasta water until that too has been smoothly incorporated.
5. Add the spag’n’spinach and stir and toss in the pan (I use a couple of forks) to mix everything together as evenly as possible. You’ll need to keep adding more of the reserved pasta water, as the pasta will keep drinking it up, so keep adding a little at a time, stirring vigorously but carefully; you shouldn’t have more than 50ml left, though you might well use it all. Taste for seasoning – you may need more salt or lemon juice – then serve, making sure you give everyone an even amount of spinach. If wished, lightly dust the top of each bowl with paprika. And, if you have half a lemon left over, you could slice it into thin wedges and give one to each person to squeeze over as they eat.