In a pan stew the onion in oil, add the spinach and continue cooking until all the liquid evaporates. Chop the spinach and season with pepper. Place the puff pastry in a 24 cm mold and perforate the bottom with a fork.
Put the rice, spinach, whipped eggs, grated cheese and salt into a bowl. Mix well. Pour the filling into the puffy pastry, level and fold in the leftover puff pastry.
Place in preheated oven at 200 ºC. (180 ºC ventilated) for about 30 minutes. At 5 minutes from the end, add the crescenza and the walnut crumble and put it back in the oven. Let it cool and serve sliced.