Cut up a small cauliflower into its flowerets, cutting the larger ones into two or more pieces, so you have all small pieces.
Bring a large pot of well-salted water to a gentle boil. Add the cauliflower and boil for about 5 minutes, until tender with just a bit of bite left. Do not discard the water.
While the cauliflower is cooking, sauté the onion (and garlic if using) in abundant olive oil until soft and translucent. Then add the anchovies, and when they've melted into the onion, add the raisins and pine nuts. If using, at this point you can also add the optional saffron or the tomato paste and/or red pepper flakes.
Transfer the cooked cauliflower to the pan, give it a toss, then add a ladleful of the cooking water. Simmer the cauliflower and its flavorings until fully tender, stirring and breaking up the cauliflower with a wooden spoon or spatula as you go. The cooking liquid should almost entirely evaporate.
Meanwhile, while the cauliflower is simmering, add the pasta to the pot where the cauliflower was parboiled, and boil until slightly underdone.
Add the pasta to the pan with the cauliflower and flavorings, along with another ladleful of pasta water. Toss and simmer until the pasta is fully al dente and the pasta is fully cooked. By this point, the condimento should have turned into a rough purée that clings nicely to the pasta as you toss them together.
At some point—any point will do—sauté the breadcrumbs gently in olive oil until golden brown. Turn off the heat and season lightly with salt.
Serve topped with the breadcrumbs