Onion, walnut and mushroom tarte tartin

4 onions
3 tbsp olive oil
200g/8oz chestnut mushrooms, halved if large
2 tsp light muscovado sugar
50g/2oz walnuts
100g/4oz blue cheese, such as Stilton, or vegetarian blue cheese
250g/9oz puff pastry

Heat oven to 200c/180c fan/gas 6. Peel the onions and cut each into six wedges through the root. Heat the oil in a large pan, add the onions, then gently fry for 20 minutes until softened and lightly coloured.

Add the mushrooms, sugar, salt and pepper and give it a good stir. Gently cook, stirring now and then for a further five minutes. Stir in the walnuts. Line the base of a 20-23cm sandwich cake tin (not loose-based) with baking parchment. Spoon over the onion mixture and press it down lightly. Crumble the cheese over.

Roll out the pastry and trim to a round, about 5cm larger than the tin. Put the pastry over the filling and tuck in the ends. Bake for 35-40 minutes until the pastry is crisp and golden. Cool for five minutes in the tin, then turn out onto a flat plate and cut into wedges. Serve with a green salad.

Can be prepared up to the baking stage a day in advance. To serve as a starter, make individual tarts in Yorkshire pudding tins.

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