Nani Mummy’s prawn karahi (curry)

Name: Nani Mummy’s prawn karahi (curry)
Cuisine: Indian, Asian
Ingredients: 1 1/2 tbs ghee (or 3 tsp unsalted butter and 3 tsp sunflower oil); 1 heaped tsp cumin seeds; 1/2 tsp nigella seeds; 1/2 tsp carom seeds (ajwain, from Indian grocers or online – substitute with cumin seeds and dried thyme), optional; 1cm (5g) ginger, peeled, finely grated; 4 large ripe tomatoes, coarsely grated, skins discarded; 1 1/2 tbs tomato paste; 1/4 tsp turmeric powder; 1/2 tsp Kashmiri chilli powder (from Indian grocers and spice specialists, substitute other chilli powder or paprika); 450g green prawns, peeled, deveined; Juice of 1/2 lemon; 2.5cm (12.5g) ginger, peeled, cut into fine strips; 1 1/2 tbs chopped coriander leaves; 1 green chilli, deseeded and finely chopped