Cut the sheet of shortcrust into wedges as if you were cutting a pie (about 5 cm along the exterior). Place a piece of cooked ham and the cheese slices, cut in such a way that they don’t extend over the edge, on the shortcrust pieces. Roll to create lots of small croissants. Brush the surface with the egg yolk to ensure the dough browns in the oven. Bake in a pre-heated oven at 180°C for about 20 minutes. Serve warm.