Portion 400 g fish into roughly 5 cm (2 in) pieces and lay them in a wide dish. Combine the marinade spices with a pinch of salt, rub the paste over the fish pieces, cover, and chill in the refrigerator for 30 minutes.
Heat 40.5 g vegetable oil in a wide frying pan over medium heat. Add 450 g sliced onion, 2.5 g curry leaf, and the whole spices for the oil, frying for 5 to 7 minutes until the onions turn a deep golden brown.
Toss in the ground coriander and sesame seeds and sauté for 1 minute until fragrant. Pour in half (250 g) of the coconut milk and simmer for 2 to 3 minutes.
Slide the marinated fish into the pan, followed by the remaining 250 g coconut milk, 240 g chopped tomato, and 250 g water. Simmer gently for roughly 10 minutes until the fish is tender and thoroughly cooked.
Scatter in 20 g chopped coriander leaf, bring the curry to a brief boil, and immediately take it off the heat. Taste and adjust salt before serving.
Steep a tiny pinch (0.1 g per 2 g turmeric) in 2 tbsp warm water; use to match the rich golden hue. Contributes an aristocratic, honeyed floral flavour rather than earthy bitterness.
Use 80% of the weight, finely shredded and browned slowly with a pinch of asafoetida. Replicates the bulk and natural sweetness in gravies without allium.
Use the same weight. The seeds are smaller and hotter; fry in hot oil until they pop, about 20–30 seconds, and reduce the heat if they darken too fast. The dish will be a little sharper.
Use 70% of the weight of whole seed, added with the other ground spices rather than fried whole. You lose the popping texture and the heat comes through more evenly.
Use 50% of the weight and stir in near the end of cooking. Adds warmth and depth since it contains ground coriander, but introduces stronger spices like clove and cinnamon.
Use equal weight; simmer gently over low heat to prevent curdling. Imparts a comparable rich texture, though it adds dairy richness without any coconut fragrance.
Use 40% to 50% of the fresh tomato weight mixed with a splash of water. Imparts a deeper red colour, thicker sauce, and slightly sweeter cooked flavour.