In a heavy cooking pot (I use a 3 qt enamaled cast iron cooking pot), warm up the mustard oil.
Add all the whole spices. Fry the spices for 10-15 seconds in hot oil taking care they don't burn.
Add the sliced onions. Over low medium heat, brown the onions for next 8-10 minutes. Stir intermittently. The more you stir, the softened onions tend to get mushy and steamy. We want crispy browned onions that will become slighty stringy at the end of cooking the pulao.
Add the minced ginger, garlic and a tablespoon of water. At this stage you can add some red chili powder, minced green chillies or slit green chilies (hot indian variety)for added kick to your pulao. I don't add green chillies because my kids do not prefer spicy rice.
Fry everything for 10-15 seconds. Add the ground lamb now. Sprinkle salt & ground black pepper (optional) over the lamb keema. Break the ground meat using a wooden spoon and mix with onions.
Now, we are going to brown the meat on high heat. Browning the meat at first pushes the moisture out that's why you will a lot of water getting released in the pot.
After about 5-8 minutes, you will see that the moisture starts reducing, the color of meat is deep brown and it is starting to glisten. We don't want to completely dry out the moisture of meat but the keema mixture should not be too watery. Please adjust time since quality of ground meat varies.
Once keema is browned, add yogurt and immediately stir to prevent the yogurt from curdling. Fry on low medium heat for 2-3 minutes until the fat of yogurt is rendered.
Next, add the cubed potato(if using) and the chopped mint leaves. Fry the potatoes and meat together for 1.5-2 minutes to get the potatoes started.