Preheat oven to 200C/180C fan/Gas6
Make the tomato sauce by cooking 3 cloves sliced peeled Garlic in 2 tbsp Extra Virgin Olive Oil for 1 minute then add 700g jar of Passata. Half cover pan and simmer for 20 minutes.
Make the cheese sauce by putting 850ml Milk, 50g Plain Flour and 50g Butter in a pan. Heat, whisking non-stop until smooth, then let bubble for 3 minutes, stirring all the time. (Sieve if still lumpy!) Cool for 5 mins then stir in 1tsp Dijon mustard, 80g grated Mature Cheddar, 20g crumbled Blue Cheese and ¼ tsp grated Nutmeg.
Boil 250g Penne Pasta and 1kg Cauliflower cut into florets in salted water until tender. Save 2 tbsp of the water and drain the rest. Melt 1 tbsp Butter in a pan, add a whole peeled Garlic Clove, 750g defrosted Spinach (squeezed dry), ¼ tsp grated Nutmeg, Salt and lots of Black Pepper. Stir for 2 mins then remove the garlic clove.
Put aside 300ml of the cheese sauce and mix the rest with the pasta and cauliflower. Divide half of the tomato sauce between 6 dishes (or one large one) and top with half the spinach mix. Cover with the cauliflower pasta mix, then the remaining spinach then the remaining tomato sauce. Top with rest of the cheese sauce and 20g grated Mature Cheddar and 20g crumbled Blue Cheese. Scatter over 25g toasted Pine Nuts. Put in oven for 18-20 minutes until bubbling. Serve with green salad and garlic bread.
Make ahead! Make up to 2 days in advance or freeze for up to a month. Defrost overnight before heating.