Balsamic onion tart

Onions are a joy, but we don’t often love them for themselves. True, they make up the base flavour for so many savoury dishes, but this tart allows us to enjoy them for what they are in all their gorgeous, sweet glory. Foolproof, this tart can be cooked ahead and is delicious warm or cold. We love it at the dinner table and it is great for picnics!