The eye-watering sharpness of a pickled onion from the fish and chip shop feels like they've been steeped in jet fuel or paint stripper. It appeals to me in the same way sour sweets or extra-hot chillies do, almost a test of endurance. But there is pleasure to be had in bitterness. The sharpness of pickles cuts through the richest meat and it's no wonder jalapenos in vinegar are a staple with nachos, or chutneys and sharp fruits go so well with roasts or cold leftovers.I often get these ideas in my head that it would be greatly frugal and Mrs Beeton-like if I made a ton of apple chutney or a vat of pickled courgettes and so on. But in truth, these jars sit at the back of the cupboard slowly softening and melting until I need the jar for something else.Knowing myself better, I find it much better to make small quantities of quick pickles for immediate use and occasional using up over the coming fortnight. Radish and mushroom for example to go with a quick poached salmon fillet for a light supper. Just a small bowlful, covered with vinegar and sugar and rested for about twenty minutes is perfect.Here, I've made half a jar of red onion slices in white wine vinegar. Perfect for our weekly tacos with the children as a final topping and also finding its way into the occasional sandwich.It's still important to sterilise the jar. But this is as easy as giving it a quick wash with hot soapy water and blasting it in the microwave for two minutes. Don't forget to remove the metal parts beforehand though.Ingredients2 red onions, peeled and finely slicedEnough white wine vinegar to cover2tbsp salt2tbsp coconut sugar or unrefined golden caster or brown sugarAbout ten peppercornsOne or two red chillies1tbsp allspice berriesA sprig of thymeA couple of fresh bay leavesMethodPut the onions in a sieve and pour over a kettle-full of boiling water to soften and blanch them.Dissolve the sugar and salt in the vinegar and add the remaining ingredients.Put the onions in a glass jar and pour over the vinegar mixture. Leave for at least half an hour before eating but it tastes even better the next day. This keeps well for about five days. And goes brilliantly with fish and seafood as well as tacos.