When mangoes are not in season and you want some fish curry with mangoes, what do you do? You are not the British Queen to feast on fruits that are not in season. What you got to do is have a June Plum tree in your yard.
I am not sure whether June Plum is the real Ambazhanga in Malayalam grown in Kerala. There is another variety similar in shape, size and texture and taste to June Plum known as Hog Plum with a bigger seed and I think that’s the original
ambazhanga. This is an excellent substitute for sour mangoes in fish curries.
Actually I have seen ambazhanga only once or twice in Kerala mostly at monasteries. Yeah, we Keralites are good at cutting down good trees like these! I am not sure whether the current generation even knows about
ambazhanga.

Anyway we have a June Plum tree in our yard and the best thing about it is it bears fruit through out the year. The tree is only 4 feet or so in height, but the fruits cover the tree.
This
link says, Very prolific, it can fruit itself to death. I vouch for that.
I made some prawns gravy with ambazhanga.
3 cups of shelled, cleaned small prawns.
1 cup of ambazhanga cut into bite sizes
1 small piece of kudampuli (depends on the variety of ambazhanga. Ours is not that sour and so I add one small piece of kudampuli as a backup)
1 sprig of curry leaves
3 tablespoons of Corainder powder, 2 tsp of chili powder, ¼ tsp of turmeric powder. Make it a paste
1 tbsp ginger diced, 6 pods of garlic diced, ¼ cup of shallots or onion diced.
Add everything mix well with salt and add 2 cups of thin coconut milk.
Boil and simmer for 10 minutes. Then just before taking off from fire, add ½ cup of thick coconut milk. Take off from heat.
Heat 2 tsp of oil, sauté 1 tsp of thinly diced shallots, 1 sprig of curry leaves, 2 red chili split. Add to the curry.
Serve hot with rice. For curries with coconut milk, storing and reheating destroys the real flavour. So always make them in small batches.