Summer fish stew with rouille

INGREDIENTS

• 6 large, raw, shell-on prawns
• 3 tbsp mild olive oil
• 150ml dry white wine
• 200ml fish stock (a cube is fine)
• 1 small fennel bulb (about 140g/5oz) halved and thinly sliced
• 1 small onion , thinly sliced
• 3 garlic cloves , thinly sliced
• 1 large potato , about 200g/8oz (I used King Edward)
• 1 orange
• 1 star anise
• 1 bay leaf
• 1½ tsp harissa paste (I used Belazu)
• 2 tbsp tomato purée
• 400g can chopped tomatoes
• handful mussels or clams
• 200g skinless, sustainably-caught white fish (I used cod loin), cut into very chunky pieces
• few thyme leaves
• 3 tbsp bought olive oil mayonnaise
• good-quality crusty bread