Sole meunière with a side

Why

Fish flesh is more delicate than the meat of land animals: the muscle fibres are short and held together by thin layers of collagen, which is less heat-stable than mammalian collagen and dissolves at a lower temperature. In fish, the main muscle protein myosin starts to change structure at around 40 °C, so a fillet is done early, and a few degrees more are enough for it to lose its juices, dry out and fall apart. For safety, the US FDA and USDA give 63 °C in the core or, without a thermometer, flesh that turns opaque and separates easily into flakes with a fork; the UK FSA uses the same sign. Cooks often leave salmon or tuna translucent inside, at around 50 °C, which is a culinary choice at your own risk: according to the FDA, pregnant women, young children, older people and anyone with weakened immunity should avoid raw and undercooked fish, and for eating raw or with a translucent centre, choose fish that has been frozen first, because freezing kills parasites (EFSA gives, for example, −20 °C for at least 24 hours), though not all other germs.

How to do it

1. Pat the fillet dry with kitchen paper before cooking so it fries rather than steams in the pan.
2. Push the thermometer into the thickest part; for fish that is safe for everyone, aim for 63 °C.
3. Without a thermometer, try a fork: the fish is done when it is opaque and separates easily into flakes.
4. Cook thin fillets for just a few minutes and keep an eye on them; in a hot pan they finish cooking even after the heat is off.
5. Prawns are done when they are firm and opaque; throw away any mussels that stay closed during cooking.
6. Keep fresh fish in the fridge for 2 days at most, otherwise freeze it, and thaw it overnight in the fridge.

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Why

Butter contains roughly 80–82 % fat, about 16 % water and 1–2 % milk solids, that is proteins and milk sugar. As it heats, the water boils first, the butter foams and spits and the temperature stays around 100 °C; once the water has gone, the foam subsides, the temperature climbs quickly and the solids settled on the bottom brown through the Maillard reaction to a nutty aroma – this is brown butter, beurre noisette. Between golden-brown and black, bitter solids there is only a moment; ordinary butter also starts to smoke at roughly 150–175 °C, so it is unsuited to fierce frying. Clarified butter is pure butterfat from which the water has evaporated and the solids have been removed before they brown; for ghee the solids are left to turn golden before straining, so the fat smells nutty. Without water and solids it tolerates roughly 230–250 °C and keeps far longer than butter.

How to do it

1. Make brown butter in a light-coloured pan or saucepan over medium heat and swirl the pan so you can see the colour of the solids under the foam.
2. As soon as the foam subsides, the specks on the bottom turn golden and the butter smells of hazelnuts, pour it straight into a cold bowl; in the hot pan it would keep darkening.
3. For clarified butter, melt butter over gentle heat, skim off the white foam and carefully pour the clear yellow fat off the milky layer at the bottom.
4. For ghee, keep the butter simmering gently until it stops spitting and the solids on the bottom turn golden, then strain it through muslin or a paper filter.
5. Keep clarified butter and ghee in a clean, dry, closed jar somewhere cool and scoop with a dry spoon; water and crumbs shorten their life.
6. For searing and frying, use clarified butter or ghee; plain butter belongs over gentle heat, and with fierce heat add it to the oil only at the end, for flavour.

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