Place 600 grams lamb shoulder, diced, in a bowl, pour over the juice of 1 lime and sprinkle with 1 tbsp smoked paprika and 1 tsp chilli powder. Stir well and leave to marinate for 30 minutes.
Heat 2 tbsp vegetable oil in a sauté pan over medium heat. Add 1 tbsp black mustard seeds and 10 whole curry leaves, and cook until the seeds start to pop.
Add 1 onion, finely chopped, 2 garlic cloves, finely chopped, 1 tbsp fresh ginger root, finely chopped and 1 green chilli, finely chopped, and cook, stirring occasionally, until the onion begins to soften.
Add 1 tsp ground turmeric, 1 tsp ground cumin, 1 tsp ground coriander, and 1 tbsp garam masala and cook for a further minute.
Turn up the heat to medium-high and add the marinated lamb. Cook the meat until browned all over.
Add 400 grams tinned chopped tomatoes, stir well and reduce the heat to medium-low.
Simmer for 30 minutes, with the lid on, until the sauce is thick and reduced. Add salt and freshly ground black pepper to taste.