My first job in a commercial kitchen was with a veteran hotel chef called John. He knew all the tricks, but also when to do things properly. Each Sunday, we made stock in a vast pot that would simmer on the stove, full of bones, trotters, herb stalks and onion skins. Once ready, it was reduced to a thick gravy and used as a base for many of our sauces.
Traditional recipes such as that stock are one way to reduce our waste, but we can also do so in other ways. Babs Behan, my friend and author of Botanical Inks, taught me how to upcycle onion skins into a fabric dye that imparts a surprisingly intense bronze colour.
To make your own, weigh some natural fabric (silk works well), then collect and weigh out half its weight in onion skins (ie, 200g cloth will need 100g skins). Simmer the skins for 30 minutes in enough water to let them move about freely, then leave to cool. Add the cloth and soak for one to three weeks, until it has a good depth of colour. Rinse in lukewarm water, wash with a PH-neutral soap, rinse again, then hang to air-dry out of direct sunlight.
Much more recently than my youthful stock-making days, I was taught by my friend and chef Justin Horne at Sativa restaurant in west London to make onion skin ash. He uses it as an avant-garde seasoning for dishes containing onions, to add smokiness, and as a bitter twist for some of his desserts. This idea might seem barmy, but ash has always been part of cooking. Even now, it is a common ingredient in many products, from ash-rind cheese and preserved herring in Europe to Pokot ash yoghurt in Kenya.
There is, however, inconclusive scientific evidence about the health/side-effects of ash, so use it sparingly, just as it is in those traditional foods. That said, there is no doubt that cooking with ash is a fun way to turn an otherwise waste product into a striking ingredient that can give a contemporary look to your food. Add a pinch to aïoli to give it a smoky flavour and intriguing grey colour, or simply finish a dish with a pinch, much as you would salt, to add a bitter, contrasting flavour and appearance.
Onion skin ash
Roast at least a handful of onion skins at 230C (210C fan)/475F/gas 8 for 30-40 minutes, or until blackened and completely charred (cook them alongside something else, ideally, to make full use of the oven). Grind to a powder, and use sparingly to add pow to all kinds of dishes.
