This has become our picnic tart of choice. The soft onions collapse into the rich, gooey blue cheese to give a wonderful savoury starter. It belongs in that small space between setting up and the entire extended family and friends converging for the main meal. —The home cook
Prepare the onion filling: Saute the onions with the salt in a large frying pan over a low heat for about 10 to 15 minutes. You want the onions to be soft and golden, with no suggestion of barbecues or burning.
Add the balsamic vinegar, apple juice and sugar. Cook over a low heat until the liquid has evaporated and the onions are browned and caramelised. Stir them so they don’t stick to the bottom of the pan. This step can take up to 45 minutes.
Take the onion mixture off the heat and let it cool down.
Assemble the tart: Break the blue cheese into small pieces and scatter them across the baked pastry base. Cover this with the caramelised onions so they fill the tart up.
Bake the tart in a 180 degrees C (350F) oven for about 15 minutes. Let it cool, and serve with some sprigs of fresh thyme.