First, a word on this dish
Think of a firm piece of boneless white fish, left for a short while in a sharp paste dominated by ajwain, then wrapped in a thick besan coating and fried until the outside shatters and the flesh stays moist. This is Amritsari fish fry, and it comes from the Punjab city it is named after, where street vendors and restaurants have long sold it, traditionally using freshwater fish from the rivers nearby. Ajwain is what you will taste first. Its faintly bitter, thyme-like edge keeps the fried coating from feeling heavy, and it is the quality that sets this dish apart from fish fries made elsewhere in India.
The story behind the dish
This fish fry belongs to Amritsar, where freshwater fish from the Beas and Sutlej river systems once filled the city's markets and street stalls. It grows out of the inland, river-based cooking of Punjab, which is quite different from the fish frying you meet on the coasts in Goa, Kerala or West Bengal. Those kitchens tend to use other fish, other spice mixtures, and often a rice-flour coating in place of besan. It helps to keep that in mind, since "fish fry" is not one recipe in India. Each region, whether on the coast or beside a river, fries what its fishermen catch and seasons it with its own local spices.
The method, in order
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Prep
Season the fish and let it rest
Dry the fish strips thoroughly with paper towels, since surface moisture makes the marinade watery and the batter slippery. Fold them gently through the ginger-garlic paste, lemon juice, crushed ajwain, chilli powder, turmeric and salt, taking care to keep each piece whole. Cover the bowl and chill it for 20 to 30 minutes. Do not leave it longer, as you might with chicken. Fish turns soft and mushy if it sits too long, particularly with lemon juice working on it.
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Prep
Mix a thick batter that clings
Stir the besan, rice flour, ajwain, chilli powder and turmeric together, then pour in water a little at a time. Stop when you have a heavy paste that just coats a spoon. It should be clearly thicker than the batter you would use for pakoras. Fish is smooth and slippery, and a thin batter will not grip it.
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Assemble
Coat the pieces
Lift each strip from the marinade and turn it through the batter, pressing lightly so the coating covers every side.
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Cook
Fry a few at a time
Warm the oil to between 175 and 185°C (345 and 365°F). Add the coated pieces gradually, a few per round and never packed, and fry each round for 3 to 5 minutes. Thin strips need less time, and thicker ones more. Flip them once. They are ready when the crust is a rich gold and sounds crisp against the spoon.
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Cook
Check that the fish is done in the middle
The fish is ready when a fork flakes it easily and the flesh is opaque right through. If you use a thermometer, look for at least 63°C (145°F) inside. Thin strips usually finish at the same moment the batter turns dark gold, but with thicker pieces you should cut or flake one open and look, instead of trusting the colour of the crust.
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Serve
Drain and eat while hot
Rest the pieces on a wire rack for a moment, then serve them right away with lemon wedges, sliced onion and a mint or coriander chutney, while the crust still crackles.
Ingredient stand-ins
Choose any firm fish without bones. Very flaky fillets tend to break apart while they marinate and while you coat them, so if this is your first try, go for something sturdier. Nothing replaces the flavour of ajwain exactly, but in an emergency a smaller pinch of dried thyme gets you somewhere near.
Making it milder or fiercer
Red chilli powder in the marinade and in the batter controls how hot this is, so use less in each if you want a milder fish. Ajwain adds a bitter, aromatic bite and not burn. You may trim it if you find the flavour too strong, though remember that it gives the dish its character.
The slip most cooks make
The first mistake is marinating too long. Lemon juice softens the flesh, and soft fillets turn to mush, so stay within 20 to 30 minutes. The second is a watery batter. It slides off the smooth fish and floats away in the oil, so keep it thick. The third is judging thick pieces by colour. The crust can reach deep gold while the centre is still raw, so break one open or use a thermometer before you assume it is cooked.
Storing what is left
Fridge or counter: Marinated raw fish should be fried the same day and kept cold until then, because raw fish keeps less well than raw meat once it has been seasoned. Fried fish can stay in the fridge for up to 2 days, although it tastes best straight from the pan, since the crust loses its crunch quickly.
Bringing it back to life: Put the fish in a 180°C (350°F) oven, or an air fryer, for 6 to 8 minutes. The dry heat recrisps the crust a little. The microwave is a poor choice, because it softens the batter and can leave the fish rubbery.
Handle with care
You are handling raw fish here, so buy it from a source you trust, keep it in the fridge until you are ready to marinate, and cook or freeze it soon after. Marinate in the refrigerator and not on the counter, and stick to the time in the recipe, because fish breaks down faster than meat in an acidic mixture. Use a separate board and utensils for the raw fish, and wash your hands, work surfaces and tools in hot, soapy water before they touch other food. Cook the fish until it flakes easily and reaches at least 63°C (145°F) inside, and put leftovers in the fridge within two hours of cooking.