Preheat the oven to 180C.
Cook the pasta until just al dente in a large pan of boiling water.
While the pasta is cooking, fry the leek for 3-4 minutes in 1 tbsp oil in a large pan then add the
garlic and continue to cook for 1 minute. Add the tomatoes, tomato paste and 1 tsp sugar and bubble for 10 minutes to cook down to a thick tomato sauce. Remove from the heat and stir through the crème fraiche, season and then stir through half the basil leaves.
Drain the pasta and add to the sauce with the spinach, stir through to wilt the spinach.
Cook the sausages in the remaining oil in a frying pan, slice on the diagonal and add to sauce.
Pour everything into a large baking dish. Whizz the cheese, bread, remaining basil, a little black pepper and 1 tbsp oil in a blender. Tip the crumbs over the pasta and bake for 10-15 mins until browned and bubbling.