I personally believe that animal fat
. Is tastier than vegetable oil. Most of French and German cooking is either Fat (Pig Fat rendered and saved as lard) or butter. I find the taste better.
. Is healthier. Northern European has traditional used fat while Mediterranean used olive oil. The former lived longer and still have less heart problems.
I get the fat from our mutton supplier. He gets goats with fat every week end. You can also use pig fat. Just heat it and boil it; as you do with butter for ghee; and then if you are particular, strain it. That is how it was done in past. You will get detailed steps for rendering fat on the net.
to make a good DUM one need a vessel of small mouth so that it can be sealed easily.
Half cooking will be done in normal method, no water is added. When it is half cook, further the vessel will be sealed to arrest water and aroma evaporation and cooked on very low heat. This is properly done on coal fire but we can do it on LPG stove too. If needed the vessel has to be kept little above the flame to reduce the heat.
Try in mud pot, it will more yummy.
DUM Biryani also made similarly. (We do not use alloo in Mutton curry.)