Put the pasta in a pan of boiling water and cook it following the instructions on the packaging. Cut the asparagus into 3 cm pieces and add these to the pasta for the last 3 minutes of cooking. Drain the pasta and asparagus, then keep them warm in the pan. (Use some of the cooking water for the tomato sauce!)
Meanwhile, finely chop the onion, garlic and celery. Heat the oil in a frying pan and gently sauté the chopped vegetables for about 5 minutes.
Chop the tomatoes (and bell pepper/carrot, if used), then add them to the pan with the capers and a drop of cooking water. Season to taste, put a lid on and cook until the tomatoes have softened, then transfer everything into a blender, add the fresh herbs & sundried tomatoes, then blitz until you get a thick sauce. Add some of the pasta’s cooking water if the sauce is too thick.
Mix some sauce with the pasta and asparagus, then serve with chili flakes or freshly ground pepper. (Use any leftover sauce for other dishes!).