01 -
Toss a bunch of salt in a big pot full of water and let it come to a hard boil. Add your spaghetti and cook it for 9-10 minutes (or whatever your package says) until it's a bit chewy. Before you drain, scoop out a mug of the water. Don't wash off the noodles afterward.
02 -
Drop the butter in a large frying pan over medium heat. As soon as it melts, add garlic and the red pepper flakes. Stir for about 60 seconds—listen for sizzle, smell the garlic.
03 -
Next up, pour in your lemon juice and half of the reserved pasta water. Toss in the drained noodles and spinach. Stir and flip everything until the spinach wilts and the spaghetti's coated evenly.
04 -
If the sauce looks heavy or the pasta's clumping, drip in some extra cooking water—up to 60 ml—until it's just right for you.
05 -
Turn off the heat. Add parmesan, lemon zest, a bit more salt, plus cracked black pepper. Mix it all up fast, then scoop onto plates and dig in while it's hot.