Add oil to a pan and pop mustard seeds (add bay leaf if using). Add onions and cook untill soft (add peppercorns if using). Add garlic, jalapeno pepper, and ginger and cook for 2 mins. Add tomatoes and cook until soft (add kasturi methi if using). Add garam masala, turmeric and salt. Add lamb and cook until meat is fully browned.Add pre-cooked peas and potatoes — stir in and heat for 2 mins. Add cilantro. Switch off heat and add optional yogurt, if you prefer a creamier taste. Stir well and then cover it up until you're ready to eat. Serve with basmati rice, brown rice, naan, or warm paav (Indian bread rolls).  (Recipe♦525)