This is actually a natural ferment - relying on the onions, water and salt and the lactic acid bacteria to come along and get the sour 'tastes like vinegar' flavour. I used a crab apple to hold the onions down under the brine and couldn't really taste any sweetness from it - but it looked good and the apple became brighter than ever and was it's own preservation project! In the photo example - I layered dill on the top and held it all down with another red onion cut to hold it down.
Enjoy on an open sandwich, chopped into salsa, in an omelette, a cheese platter, on liver paste and rye...
This recipe is from my book 'Ferment for Good, Ancient Foods for the Modern Gut' on p78. Hardie Grant. )
NOTE: You'll need a clean 1 liter jar. Use as many onions as you need to fill the jar to 3/4 full. —Sharon Flynn
Make a brine with the salt and water. If the salt is fine enough it will dissolve by stirring.
Pop the garlic, mustard seeds, sprigs of herbs into the jar.
Pour the brine over the onion, leaving some room- a couple of inches- between the brine and the lid.
Weigh down with whatever you have at hand to keep the onions under the brine - lever down with something like a whole small apple, or fermenting weights, another onion cut in half to hold them down. (Or just keep an eye on it)
Leave to ferment on your bench for 5 days - taste and if not sour enough then let sit longer. When it's to your liking, take out the weights and pop into the fridge.