I have not been able to find any malt vinegar where we live in Turkey, usually used when making pickled onions, but have found that the darkest red grape vinegar that I can find works just as well.
500g shallots or smallest onions you can find, (up to ping pong ball size will work ok)
1tsp black peppercorns per jar
1tsp mustard seeds per jar
black grape or malt vinegar
Peel the onions and put into the jars, if you have to use two jars but don't have enough to fill them I just divide the onions between the two.
Then add 1tsp of black peppercorns and 1 tsp of mustard seeds to each jar.
Fill with vinegar until the onions are completely covered.