Shallots and Onions

What is the difference between shallots and onions and can they be substituted for one another? Shallots and onions are both members of the lily family – along with leeks, chives and garlic – but are not the same thing at all.

Shallots are much smaller than onions, but are distinct from baby onions and have a more subtle flavour. The best are almost purple in colour and form the basis for a number of classic dishes and preparations like beurre blanc. Shallot vinegar is also a fine accompaniment with oysters.