Use either tamarind pulp or the substitute I'm using for the video, comes out great either way. Fast, cheap and tasty and lots of nutritious food.
1 x 540 ml (18oz) can kidney beans
1x 540 ml(18oz) can black beans
1 x 400ml (13.5oz) light coconut milk
1 tsp (5ml) curry powder
1/2 tsp each (2.5ml) onion & garlic powder
1.5 inch cube tamarind pulp in hot water
OR
60 ml (1/4 cup) rice vinegar
60 ml(1/4 cup) light brown sugar
6 cups cooked rice