1. Wash the onion. Clear. Cut into large pieces.
2. Peel the garlic.
3. Wash the mushrooms. Cut into large pieces.
4. Duxel: bring the onion and mushrooms in a blender to the consistency of pate.
5. Fry the mushroom pate in a frying pan without oil for 15-20 minutes. Stir regularly. Add pepper to taste.
6.Add salt to the beef tenderloin.
7.Heat the butter and olive oil in a hot frying pan. Add the rosemary and garlic.
8. Put the beef in the frying pan and seal all the juices. Fry for 1 minute on all sides. Reduce the heat by half. Fry for about 10 minutes on all sides.
9. Spread a piece of food wrap on the work surface of the table. The size should be such that your piece of meat can be wrapped 2 ½ times.
10. Place the bacon slices tightly together on the food wrap.
11. Put the mushroom pate on top of the bacon in an even layer.
12. Lubricate the beef with mustard.
13. In the middle of the pate, we spread our beef. Wrap the beef tightly and carefully to make a roll. Without removing the food wrap from the roll, we send it to the freezer for 30 minutes.
14. Repeat step 9 with the food wrap.
15. Put a sheet of puff pastry and roll it out a little to the size that it would be free to wrap our roll.
16. We take out our roll from the freezer, remove the food wrap from it and wrap it with a sheet of puff pastry. We do not remove the food wrap from the dough! We send it back to the freezer for 30 minutes.
17. Remove the roll from the freezer. Cover with egg yolk on all sides. We make a pattern on the dough with a knife. Sprinkle with coarse sea salt.
18. Place in a baking dish and place in the oven at 356 ℉ (180 °C). Cook until the dough is golden and crispy.
Serving table: Serve the dish hot. Cut into pieces 5-7 cm thick.