It is difficult to say Naga because the recipe you make, as posted, uses a lot of pre-made ingredients. Without going into analysis of each of these an exact match wont happen, However, based on the facts that it has Tomato, Lemon Juice and Coconut, it would appear to be a fair match to the book dish titled Kukul Mus Thakkali (chicken and tomato curry). A noticeable difference is the absence of sugar but you could use some jaggery or brown sugar if desired.
Edited: I just realised that another difference is the near complete lack of onion. Other than 50 g shallots there is no onion in the Sri Lankan dish. I guess there isn't a whole lot of onion in only 300 ml of Base Gravy in the Ceylon dish so possibly not that significant.
Ingredient list follows. The chicken is marinated in the spices and vinegar for 20 minutes and then it's all cooked in the traditional curry method. Hot oil, aromatics / veggies, followed by tomatoes, then the marinated and spiced chicken pieces. After 5 minutes add the coconut milk, boil then simmer till cooked through. Probably 20 minutes to 1/2 an hour being on the bone. Garnish and serve.
Ingredients.
1.3 kg chicken washed and jointed.
3 Tomatoes
50 g Shallots
1 fresh chilli
3 slices ginger
2 cloves garlic (garlic and ginger ground to a paste)
3 cardamoms (ground)
2 cloves (ground)
1 tsp chilli powder
1 cm cinnamon stick (my comment; very small amount and the method doesn't mention where to use it. Possibly ground)
2 tsp paprika
1 tsp salt
3 tsp curry powder
1/2 tsp fenugreek ( I'm assuming seed but could be leaf)
2 tsp brown vinegar (quite a small amount to cover 1.3 kg of chicken as a marinade. May need a bit more. Possibly meant to be TBSP)
75 ml oil
sprig of curry leaves
1/2 stem of lemon grass
300 ml thick and thin coconut milk (I'm assuming it's 300 ml total but not sure)
a sprinkle of curry powder to finish (could probably use a GM or Kitchen King or Tandoori Masala)
juice of 1/2 lime prior to serving.
The dish you make is clearly a BIR dish, as you'd expect, but it is usually possible to convert traditional curry into BIR method by ingredient analysis and substitution. I've done it with several dishes and the side by side test end results are quite similar.
I'll have to give the Ceylon a try sinces you recommend it as your family favourite. At the moment our favourite dish is the Lamb Korma Balti. That is the good wife and myself. If I tell Mrs L it's a Sri Lankan curry she'll be in.