Lay the puff pastry pockets out next to one another, and leave to thaw for approx. 10 – 15 minutes. Sort, wash and drain the fresh spinach. Alternatively, leave the deep-frozen spinach to thaw. Finely chop the onion, and steam in the butter until translucent. Add the spinach leaves, allow the liquid to boil, and season with salt and pepper.
Crush the feta with a fork, season with salt and pepper, and stir in the pesto. Roast the pine nuts in an ungreased pan until golden-brown. Pour the spinach, the feta mixture and pine nuts onto the pastry sheets, and form into pockets. Press the sides down well, then coat the pockets with egg yolk. Bake on the middle shelf of a preheated oven at 200 °C for approx. 20 minutes.

For the side salad, sort, wash, clean and thoroughly drain the lamb’s lettuce. Wash the cherry tomatoes, cut into quarters, and season with salt and pepper. Arrange the lettuce and cherry tomatoes on the plate.
Finely dice the onion. Pour the balsamic vinegar, mustard, olive oil, diced onion, salt and pepper into a screw-top jar, and shake well. Season to taste once again, and drizzle over the salad. Sprinkle with cashew nuts, and serve with the freshly baked puff pastry pockets.