Preheat oven to 190 °C (370 °F).
Heat 50 g (1¾ oz) butter in a frying pan. Add onion and garlic and sauté until caramelized (5-10 minutes).
Add spinach, salt, nutmeg and cream, mix well and set aside.
Heat the remaining butter in a frying pan. Add breadcrumbs and sauté until golden brown. Set aside.
Cover the bottom and sides of a cake pan (Ø 21 cm, 8'') with baking paper.
Roll out a sheet of puff pastry and place it in the pan so that it covers the bottom and sides of the pan.
Cover the bottom with the breadcrumbs-mixture, top with the spinach and finish with a layer of ricotta.
Top the cake with the second sheet of puff pastry, cut off the excess dough and press the edges together and roll towards the inside of the pie.
Brush the pie with cream and top with salt flakes and fresh thyme.
Bake for 35 minutes at 190 °C (370 °F).