Take the dough out of the tins, roll it out, press 2 pieces of dough together at each seam and roll it out into a rectangle (20 x 15 cm). Spread the dough plates with mustard and cover each with 1 slice of ham.
Wash the chives, cut into fine rolls and sprinkle on the ham. Cover each pastry sheet with 3 slices of cheese and roll up from the narrow side. Place on a baking tray lined with baking paper.
Whisk the egg yolk with milk and spread it on the roll. Bake in the preheated oven (electric oven: 200 °C/ gas: level 3) for approx. 25 minutes. Cut into slices and serve warm.