Put a large saucepan of water on for the pasta.
When the pasta water has come to the boil, salt it - it will rise up excitedly. Once it's calmed down again, drop in your spaghetti and cook according to the packet instructions, though start checking a couple of minutes before it says.
Into a large pan, add the olive oil and the anchovies, and warm slowly, stirring and pressing down on the anchovies until they seem to melt into the oil.
Take off the heat, peel and mince or grate in the garlic, add the chilli flakes and diced peppers, then put back on the heat, this time turned up to medium, and stir for a couple of minutes before adding the spinach leaves. Turn the leaves around in the chilli-flecked anchovy oil for a minute or so to soak up the flavour until they are wilted.
Use a pasta fork or tongs to add the cooked spaghetti straight to the waiting pan of spinach and peppers. It doesn't matter if the pasta is dripping with water, as that starchy liquid will help thicken your sauce. Turn the spaghetti well in the spinach, pepper and anchovy mixture; you may need to add up to 4 tablespoons (60ml) of cooking water as you toss everything together; go slowly, and stop when the spinach seems to turn into a sauce that cleaves to the strands of spaghetti.
Grate over about 2 tablespoons' worth of Parmesan or Pecorino Romano and toss again, then give a generous pour of olive oil, and do likewise. Taste to see if you want more cheese or oil, and proceed accordingly, then turn into a warmed bowl or bowls, and bring the cheese, a grater and the bottle of olive oil to the table with you.
