Preheat the oven to 220°C. Peel and thinly slice the red onions, then peel the shallots and cut into quarters. Put both aside.
Lightly flour a work surface, then cut the pastry in half and roll out each piece to a rectangle of about 30cm x 15cm. Cut two large rounds from each, using a 13–15-cm saucer as a guide, and place the pastry rounds on a large baking tray.
Beat the egg lightly and brush over the pastry, taking care not to let it trickle over the edges.
Pile a quarter of the onions and shallots in the centre of each round, leaving a border of about 2 cm all round. Place 3 sprigs thyme on top of each pile.
Brush the onion and shallot mixture lightly with the olive oil and season to taste with salt and black pepper. Put the pastries into the oven and bake for 20 minutes, or until they are puffed up and golden brown.
Meanwhile, prepare the salad. Rinse, dry and trim the spinach leaves and watercress and put both into a serving bowl. Roughly chop the walnut pieces and add to the salad leaves.
Remove the rind from the Stilton and put the cheese into a small bowl. Pour in the cream and mash the two together thoroughly. Then beat in the walnut oil and sherry vinegar until smooth. Season to taste with a good grinding of black pepper (the Stilton should be salty enough, so no further salt is necessary). Pour the dressing over the salad and toss gently.
When the pastries are cooked, serve them on individual plates, accompanied by the bowl of dressed salad on the side.
If you prefer a milder, blue cheese flavour, you can replace the Stilton with either a blue Brie or a Blue Castello.
NUTRIENTS PER SERVING:
good source of vitamins A, B group, C, E and folate, and calcium.
Using a stout wooden spoon and a sturdy bowl makes it an easy job to mash the cheese and cream together when you are preparing the salad dressing.