Black Onion Seeds are not from onions at all but from a species of buttercup! The seeds, once dried are crunchy and have a slight onion tang, hence the name. They are also known as Kalonji Seed or Nigella Seed, My recipe in The Library of Rosie's Preserving School is for Blood Orange and Black Onion Seed Cheese or Paste - absolutely delicious eaten with cheese and the crunchy seeds give a great accent flavour