Malabar prawn biryani

Ingredients

• 500g large prawns, shelled and deveined and washed
• ½ tsp turmeric powder
• ½ tsp chilli powder
• ½ tsp freshly ground black pepper
• Salt to taste
• 400g Basmati rice, well washed
• 750ml water
• 1 tbs vegetable oil
• 2 tbs ghee or butter
• 2 small onions, very finely sliced
• 1-inch cinnamon stick
• 10 black peppercorns
• 6 cloves
• 6 green cardamom pods
• ½ lemon
• 8 curry leaves, roughly torn
• 2 tbs vegetable oil, plus 2 rounded tbs ghee or butter
• 3 small onions, finely chopped
• 12 fresh curry leaves (add a few extra if dried)
• 8 large cloves garlic, grated into a paste (around 2 tbs)
• 30g ginger, peeled and grated into a paste
• 1 tsp powdered fennel seeds
• 1 1/2 tsp garam masala
• ½ tsp red chilli powder or to taste
• 1 tsp turmeric powder
• 2 small-medium tomatoes, chopped
• Handful of fresh chopped coriander plus 2 tbs chopped for assembly
• 2 tbs chopped mint leaves
• 20g butter
• ½ tsp garam masala