Ceviche

Boil the sweet potato whole, with the skin on, in salted water for 30 to 35 minutes, until a knife slides in easily. Add the corn cobs to the same pan for the last 10 minutes. Drain and let them cool. Peel the sweet potato and cut it into thick rounds, and cut each corn cob into 2 or 3 rounds. They are served at room temperature.

Halve the red onion and slice it paper thin. Soak the slices in a bowl of iced water for 10 minutes to take away the harsh edge, then drain and pat dry.

Raw fish must be impeccably fresh, so buy it on the day and ask at the fish counter for fish that is suitable for eating raw (fish for this is often frozen first to kill parasites). Keep it in the fridge until the last minutes. Pat it dry, check for pin bones and cut it into even 2 cm cubes so that every piece cures at the same speed. Return to the fridge. Raw fish is not suitable for pregnant women, young children, older people or anyone with a weakened immune system.

Squeeze the limes gently, as pressing hard releases bitter oils from the pith; you need about 150 ml of juice. Put it in a blender with the garlic, ginger, celery, one of the chillies (deseeded for a milder sauce), half of the coriander, stems included, and ¾ teaspoon of the salt. Blend for 20 seconds.

Strain through a fine sieve into a chilled bowl, pressing on the solids. Taste it: it should be sharp, salty and hot. It will mellow slightly once it mixes with the fish. Keep it cold.

Tip the fish into a cold bowl, sprinkle with the remaining ¼ teaspoon of salt and pour over enough leche de tigre to nearly cover it. Stir gently without breaking up the cubes.

Leave for 5 minutes for a soft, translucent centre, or up to 10 minutes for a firmer bite. The outside turns opaque white while the middle stays slightly glassy. Left much longer, the acid makes the flesh chalky and rubbery.

Divide the fish between chilled shallow bowls with a ladle of the leche de tigre each. Top with the red onion, the second chilli sliced thinly and the remaining coriander, roughly chopped. Serve straight away with the sweet potato and corn beside it. Eat within 20 minutes of curing and do not keep leftovers.