One-pot Goan lamb shank curry with coriander

Ingredients

• 4 lamb shanks
• 2 tablespoons ground coriander
• 2 tablespoons ground turmeric
• 2 tablespoons ground cumin
• 1 tablespoon chilli powder
• 2 red onions, roughly chopped
• 1 bunch coriander, leaves picked, roots and stems reserved
• 7 centimetre piece ginger, peeled, sliced
• 4 garlic cloves, peeled
• 2 tablespoons vegetable oil
• 1/3 cup vindaloo curry paste
• 2 tablespoons tomato paste
• 15 curry leaves
• 2 litres water
• yoghurt, naan bread to serve