Cut the meat into medium size pieces, wash and allow to drain on a colander. Wash and peel the potatoes, cut them into thin wedges, apply some salt to the wedges and keep the vessel a bit slant so that excess water gets drained.
Grind these ingredients to a fine paste using a little water - dry red chilli skins, peppercorns, cumin, turmeric, ginger, garlic, green chilli, tamarind, almonds, raisins, onions, cloves and cinnamon. Retain the masala water (from the mixer grinder). Grind the tomatoes separately - keep this purée aside.
In a pressure cooker heat some oil or ghee and fry the sliced onion till it turns slightly golden in colour. Add the ground masala and fry for a few minutes and then add the tomato purée, fry a little and add the masala water. Fry on low fire for about 5-7 minutes, stirring every now & then.
Add the meat pieces and mix well. Add about 1/4 cup of water if necessary (just about enough to cover the meat or more if you require gravy). Add salt to taste and vinegar if you wish. Mix well
Cover the pressure cooker with the lid, place the weight (whistle) and cook on full flame till the first whistle goes off (should take about 7-8 minutes). Reduce the flame completely and cook for a further 13-15 minutes (if you are cooking tender Mutton) or 20-25 minutes (if you are using tender Beef). You may need to cook for an extra 5-7 minutes if the meat is not tender - please use your discretion. Turn off flame and wait for the pressure to get released on its own (whistle becomes loose). Open the lid, mix well.
In a frying pan fry the salted potato wedges (see step#1) till they turn just about golden in colour. Fry on both sides and add them to the cooked meat. Garnish with chopped coriander (optional)
Serve hot with rice, chapathis or dosas