Bring a large pot of generously salted water to a rolling boil.

Finely grate the zest from 1 lemon, then cut the lemon in half.

Add 400 g spaghetti to the boiling water and cook until very al dente, about 2 minutes less than the package instructions.

Melt 250 g butter in a large skillet over low heat without browning it.

Add 60 g Italian anchovies to the melted butter and stir until they dissolve into the sauce.

Reserve 240 ml pasta cooking water, then drain the al dente spaghetti.

Transfer the drained spaghetti to the skillet and toss it with the anchovy butter.

Add the reserved pasta cooking water a little at a time, tossing until the sauce becomes creamy and coats the spaghetti.

Turn off the heat and toss in the lemon zest with juice from half the lemon.

Season with black pepper and salt only if needed, then serve immediately.