Heat the olive oil in a large skillet or casserole (Dutch oven) over a medium-high heat.

Add the shallots and sliced garlic and season with salt and pepper.

Cook, stirring occasionally, until the shallots have become completely softened and caramelised with golden-brown fried edges, 15–20 minutes.

Add the chilli flakes and anchovies. (No need to chop the anchovies; they will dissolve on their own.) Stir to melt the anchovies into the shallots, about 2 minutes.

Add the tomato purée and season with salt and pepper.

Cook, stirring constantly to prevent any scorching, until the tomato purée has started to cook in the oil a bit, caramelising at the edges and going from bright red to a deeper brick-red colour, about 2 minutes.

Remove from the heat and transfer about half of the mixture to a resealable container, leaving the rest behind.

Bring a large pot of salted water to the boil.

Cook the pasta until very al dente (perhaps more al dente than usual).

Save 480ml of pasta water, then drain the pasta.

Transfer the pasta to the pot with the remaining shallot mixture (or a skillet if you are using the leftover portion) and 250ml of pasta water.

Cook over a medium-high heat, swirling the skillet to coat each piece of pasta and using a wooden spoon or spatula to scrape up any bits on the bottom, until the sauce is reduced and a little sticky, perfectly coating each strand of pasta, 3–5 minutes.

Combine the parsley and the finely chopped garlic in a small bowl and season with flaky salt and pepper.

Divide the pasta among bowls or transfer to one large serving bowl and top with the parsley mixture and a few more chilli flakes if you like.