Defrost a sheet of shortcrust or puff pastry. Halve a good handful of peeled shallots. Cover the base of a saucepan in Balsamic vinegar and cook the onions until they take the vinegar’s colour. Tip these into a pie dish and fill any gaps with grated Parmesan. Cover the top of the onions with cheese too – you can add flaked chilli at this stage if you like. Put the pastry over the onions, paint on egg wash and bake for 25 minutes at 180C. Once browned, use a plate to tip the tart put of the tin – the pastry will be on the bottom. Serve with a salad or on its own.