Butter and vegetable oil for frying
2 medium-sized onions, peeled and finely chopped
1 garlic clove, crushed with 1 tsp salt
1 small piece fresh root ginger, very finely chopped, or 1 tsp spoon ground ginger
1 tsp spoon turmeric
1/2 tsp chilli powder
1 tbsp ground coriander seed
1 tsp spoon ground mustard seeds
3/4 - l kg ()1 1/2 - 2 lb chuck steak, trimmed of fat and diced
226 g (8 oz) packet frozen whole leaf spinach, thawed and dried by heating gently in a saucepan over low heat
2 x 141 g. (5 oz) cartons natural unsweetened yogurt