Clean the cauliflower, cut into florets and cook in salted water until cooked (save the water!). Pre-cook the pasta, drain and rinse. Put both aside.
Dice the bacon and onion, then fry in the butter. Add the flour and prepare a roux. First add the tomato paste and roast briefly, then deglaze the cauliflower with a little cooking water, bring to the boil and add enough water until the soup is only slightly creamy. Season with ketchup, salt and pepper, season with garlic if you like.
Add the pasta and cauliflower and let it get hot quickly. Season again to taste and mix in herbs to taste.