Pre-heat your oven to 180℃
In a large pan heat water and add some salt. Once boiling drop in the cauliflower broken into small florets (minus the leaves) along with pasta. Boil until al dente.
In the meantime heat 2 tbsps of butter and once melted add 2 tbsps of flour and start frying until smooth paste is created. Then start adding the milk gradually on a low heat. Then add the nutmeg, salt and pepper to taste and bring to boil until your sauce thickness slightly. Once a bit thicker add all the cheese (Except parmesan) and mix well until melted. Transfer into oven proof dish or skillet and add the cauliflower and pasta. using a teaspoon dollop the fennel and olive paste in various places and stir slightly.
For the crispy topping melt 1 tbsp of butter and add the breadcrumbs along with chopped cauliflower leaves, chopped garlic and parmesan cheese and fry until golden brown and crispy. Top your Mac & Cheese with the crumble and put in the oven for 15-25 minutes until nice and bubbly