Heat the olive oil in a pan over medium-low heat. Add the sliced onion with a pinch of salt and cook slowly for 15–20 minutes until soft and caramelised. Stir in the balsamic vinegar and cook for another minute.
Heat the oven to 200°C (fan). Place the puff pastry sheet onto a baking tray lined with baking paper. Score a border about 1.5 cm around the edge.
Spread the caramelised onions evenly over the pastry inside the border. Arrange the figs on top and scatter with walnuts and crumbled Newington Blue.
Bake for 18–22 minutes until the pastry is golden and crisp.
Scatter with fresh thyme leaves and a little black pepper.