Cut the meat into cubes.
Soak chillies in vinegar and water for 10 minutes.
Put chillies, vinegar, water, ginger and garlic into a food processor/electric blender and blend until smooth.
Add Rubyspice Vindaloo Spice mix. Blend, then pour mixture into beef cubes and marinate, covered, for 2 hours or ideally, overnight.
Heat ghee and fry onions gently until soft and golden brown. Stir frequently to prevent browning onions from sticking to bottom of pan.
Add marinated meat to browned onion mixture and keep stirring meat cubes until meat changes colour.
Add all marinade mixture if any left in the bowl. Cover pan and simmer on low heat until meat is meltingly tender, approx. 2—3 hours. Stir in the sugar (if using).
P.S. The Vindaloo Spice mix has salt added.