Place the ribs in a large, wide saucepan. Cover with water and add the onion, garlic, fennel seeds and star anise. Bring to a boil, then reduce the heat and simmer very gently for three hours ...
Add the celery and fennel and fry until softened. Season with salt and pepper. Add the tomatoes, smoked paprika, star anise, saffron and tomato purée. Stir and cook for 5–10 minutes to soften.
Add fennel, season with salt and pepper, and cook until fennel starts to soften, 6-8 minutes more. Stir in garlic and thyme sprigs, and season with salt. Cook for 2 minutes, then remove pot from heat.