In a big pan put the Cotechino di Modena PGI, the celery, and the carrot and cover them with cool water. Cook on the low heat for about 30 minutes, then remove the skin of cotechino, cut it into rounds and let it cool. Meanwhile, boil the chicory and pan fry it with the butter for 2 minutes, adding salt and pepper. Preheat the oven, roll out the puff pastry and place over it the chicory and the cotechino. Wrap and brush the dough with a beaten egg yolk. Place everything in a nonstick baking tray and cook in the oven for 30 minutes at 350 F. Finally cut the puff pastry into slices and serve.