Blue cheese and sweet onion tart with watercress and walnuts

Method

1. On a lightly floured surface, roll the pastry into a thin 30cm x 38cm rectangle. Carefully lift it onto a lightly buttered baking sheet, then prick all over with a fork. Chill in the fridge for at least 20 minutes.

2. Preheat the oven to 200°C/fan 180°C/gas 6. Heat the oil in a large frying pan over a medium heat, then add the onions and salt. Fry gently for 10 minutes, stirring now and then. Sprinkle over the sugar, then continue to cook, stirring more regularly as they become softer, allowing them to catch slightly on the base of the pan before stirring, until they are richly caramelised. Season to taste, then set aside.

3. Bake the pastry for 20 minutes. Remove, carefully flip, then bake for 5 minutes. Remove the tray from the oven again, then flip the pastry back over and set it aside for a few minutes until it deflates slightly.

4. Spread the pastry base with the onions, leaving a 2-3cm border around the edges. Top with the cheese, then bake for 5 minutes until the cheese has just melted.

5. Remove the tart from the oven and slide it onto a large wooden board. Scatter over the watercress and toasted walnuts, then slice the tart and serve straightaway, while the pastry is still warm and crisp.