1 Lay the puff pastry sheets side by side to thaw. Peel the onions and cut into rings. Sweat in 3 tbsp butter until soft, then sprinkle with sugar and fry for a further 2 minutes or so. Season with salt and pepper and take out of the pan.
2 Crumble the cheese. Peel, halve and core the pears and cut the halves into fans. Whisk the egg yolk with 1 tbsp water and brush the edges of the pastry sheets.
3 Arrange the onions, cheese and pear halves on the pastry sheets, leaving a border of approximately 0.5 cm free at the edges. Brush the pears with the rest of the butter.
4 Bake in an oven preheated to 200°C (180° fan) | 400F | gas 6 for 20 minutes until puffed.