Tear the stale bread into chunks and pulse in a food processor until you have rough, uneven crumbs about 3-4 mm in size. Do not over-process to fine powder.

Warm the olive oil in a wide, heavy-bottomed skillet over medium-low heat. Add the garlic slices and cook for 2 to 3 minutes until pale gold and fragrant.

Add the anchovy fillets and press them with the back of the spoon for 1 to 2 minutes until they dissolve completely into the oil.

Remove and discard the garlic slices. Add chili flakes if using and stir briefly.

Add the breadcrumbs to the pan in an even layer. Toast over medium-low heat, stirring constantly, for 8 to 12 minutes until uniformly deep golden and crisp. The crumbs should smell nutty, not sharp. Remove from heat and set aside.

Bring a large pot of water to a rolling boil. Add the coarse salt and cook the spaghetti according to packet instructions until al dente.

Before draining, ladle out about 120 ml of pasta cooking water and set it aside.

Drain the pasta, then immediately return it to the pot or add it directly to the skillet with the breadcrumbs off the heat.

Add the finishing olive oil and a splash of reserved pasta water (about 3 to 4 tbsp). Toss quickly and firmly for 1 minute until the crumbs coat every strand evenly. Add more pasta water if the mixture looks dry.

Taste for salt, scatter parsley over the top if using, and serve immediately in warmed bowls with a final thin drizzle of raw olive oil.