For the tomato sauce, cook the sliced garlic in the oil for 1 min, then add the passata. Season, half-cover the pan and simmer for 20 mins until rich.
Meanwhile, make the cheese sauce. Put the milk, flour and 50g butter into a pan. Heat, whisking non-stop, until smooth, then bubble for 3 mins, stirring to make sure any flouriness is lost. Cool for 5 mins, then stir in the mustard, most of the cheddar, half the blue cheese and half the nutmeg.
Boil the penne and cauliflower for 8 mins in salted water until the pasta is almost cooked and the cauli is tender. Keep 2 tbsp water from the pan, then drain. Melt 1 tbsp butter in a pan, add the whole garlic clove, spinach, remaining nutmeg, salt and lots of black pepper. Stir for 2 mins, then remove the garlic clove.
Set aside 300ml cheese sauce and mix the rest into the cauli and pasta. Divide half the tomato sauce between 6 dishes and top with some spinach. Fill with cauli mix, top with more spinach, then the rest of the tomato sauce. Top with the cheese sauce, cheeses and pine nuts. Cover with cling film, cool and chill for up to 2 days or freeze for up to 1 month. To cook, defrost if frozen. Heat oven to 200C/ 180C fan/gas 6. Cook on a baking sheet for 18-20 mins until golden and bubbling. Good with green salad or garlic bread.
