Heat the EVOO in a soup pot over medium to medium-high heat. Melt the butter into the oil, then add the garlic, rosemary and onions. Season with salt and pepper. Cook, partially covered, to soften, about 10 minutes. Add the wine and deglaze, then add about 1/2 cup stock and the whole head of cauliflower. Cover the pot and steam the cauliflower until very tender, about 15 minutes. Uncover and break up with a potato masher, then add the remaining stock, milk and potatoes. Season with a little nutmeg and cayenne, to taste. Bring to a boil and cook until the potatoes are tender, 10 minutes or so. Puree with an immersion blender, then simmer over low heat to thicken to desired consistency, and adjust seasonings. Cool and store for a make-ahead meal.
For the breadcrumb topping:
Heat the EVOO, 1/4 to 1/3 cup, in a skillet over medium heat. Add the anchovies and stir until they melt away into the oil. Lower the heat, and add the garlic and some black pepper and stir a minute or 2. Add the breadcrumbs and cook until deeply fragrant and well toasted. Remove from the heat. Cool and combine with the parsley and cheese. Store in an airtight container.
Serve the soup in shallow bowls topped with the breadcrumbs.