Clean, wash and drain the spinach. Peel and finely chop the onions. Peel and finely dice the garlic. Heat oil in a large pot, fry onions until translucent, add garlic, fry briefly, add spinach.
Collapse in a closed pot. Season with pepper. Pour into a sieve, drain well and allow to cool. In the meantime crush cheese with a fork. Beat the eggs with the whisk of the hand mixer.
Mix cheese and eggs. Let the dough sheets rest at room temperature for ten minutes. In the meantime melt butter in a pot. Squeeze the spinach with your hands and mix it with the egg and cheese mixture. Roll out the dough sheets.
Place a sheet of dough on a damp, well-expressed tea towel. Brush with some butter, place the second pastry sheet on it, brush with butter again, place the third pastry sheet on it. Roll up the rest of the pastry sheet.
Cut the dough into four equal pieces. Sprinkle each piece with 1/2 tablespoon breadcrumbs. Place one tablespoon of spinach mixture in the middle of each piece, fold over the protruding edges of the dough from the sides to the middle, or fold it over.
Process the remaining dough sheets (1 x 3, 1 x 4 sheets) in the same way. Place on two baking trays lined with baking paper. Whisk egg yolk and cream. Carefully brush the dough pockets with it. Bake in the preheated oven (electric range: 175 °C/ convection oven: 150 °C/ gas: level 2) for 25 to 30 minutes.
Remove from the oven and serve immediately.