Defrost puff pastry, roll it out to a thickness of 3 mm.
Using a pizza cutter (or a simple sharp knife), cut out triangles.
Spread the filling on the wide part and roll up the croissants.
Put on a baking sheet and cover with a towel. We leave for an hour.
Preheat oven to 180 degrees. Separate the yolk from the protein, grease the raw croissants with the yolk and put in the oven for 25 minutes. Voila!