Wash meat, drain and cut into 4-cm long, 1-cm wide strips.
Place in a pressure cooker with vinegar, salt, ¾ cup water and half the ginger and turmeric, and cook under pressure for 30 minutes.
Separate meat from stock and set aside.
Heat 1 ½ tbsp oil in a pan, add onions, garlic, green chillies, curry leaves and remaining ginger, and fry till onions turn translucent. Remove from oil and set aside.
Pour remaining oil into pan and sprinkle in mustard seeds. When they start sputtering, sprinkle in flour, coriander powder, pepper and remaining turmeric, and fry for 2 minutes, stirring constantly.
Add meat and sauté for 5 minutes.
Stir in reserved onion mixture and cook till gravy thickens.
