River Cottage

Preheat the oven to 190C/Gas Mark 5. Roll out the pastry to a 3–4mm thickness and cut out a 20cm circle. Wrap the pastry disc and place it in the fridge.

Peel the onions and slice each one into 6 or 8 wedges, keeping them attached at the root end. Heat the butter and oil in a 20cm tarte tatin pan or ovenproof frying pan over a medium heat. Add the onions, arranging them roughly in a concentric pattern. Sprinkle with salt and pepper and cook for about 15–20 minutes, turning once or twice, until they are fairly tender, and starting to caramelise around the edges.

Trickle the balsamic vinegar over the onions and cook for a couple of minutes more, so the vinegar reduces a little. Remove from the heat�and make sure the onions are fairly evenly spread around the pan.

Lay the pastry disc over the onions and put the pan into the oven. Bake for 20 minutes, until the pastry is fully puffed up and golden.

Invert the tart on to a plate, so the sticky caramelised onions are facing up, on top of the crispy pastry. Serve straight away, ideally with a green leafy salad. You could also crumble or grate over a favourite cheese.