Preheat the oven at 200°.

Use a mortar and pestle to grind the rosemary, garlic, pepper and the olive oil until it becomes a smooth paste. 

Salt the meat on both sides and brush the interior with the spice mixture. Wrap the meat and keep closed with 2-3 toothpicks, if necessary. 

Place the meat on the puff pastry sheet (which you have rolled out a little bit with a rolling pin). Wrap so that the sealed edges of the sheet are under the meat. 

Brush everywhere with the beaten egg and bake for 10' at 200°. Lower the heat at 180° and bake for 1 1/2 hour. In the middle of baking time wrap with aluminum foil. 

Remove the meat from the oven and let it rest for about  15 ' before you cut it. Cut it into slices and serve with potatoes in the oven.