Dry the meat. Salt beef tenderloin. In a frying pan over high heat, heat olive oil and brown the meat on all sides well. Put away for cooling. Keep the pan with sticky juice to prepare the sauce.

Preheat the oven to 240 degrees with the grill at the bottom. Cover a baking pan with baking paper. Cut the puff pastry so that a large piece is 500 grams and a small piece is 150 grams. Roll out a large piece with a rolling pin to make a rectangle 3-4 mm thick, large enough to wrap the tenderloin in it.

In the middle of the pastry put slices of foie gras. Put on foie gras tenderloin without dressing. Pinch the dough so that the meat is wrapped in it (there should be no access to air).

Brush the dough with yolks that mixed with water. Put the beef in the dough on the baking sheet with the seam down and put in the refrigerator.

Roll out a rectangle 3-4 mm thick and with a length of dough from the second piece of dough. Cut into strips 1-1.5 cm wide. Remove the beef in the dough from the refrigerator and grease again with the yolk. Spread on it strips of puff pastry to make a wire rack. Grease with the yolk. Put in the oven and bake for 25 minutes at a temperature of 220 degrees. Remove from oven and let stand for 15 minutes before serving.

To prepare a gastrique sauce, put sugar in a small pan and caramelize it without adding water. Pour vinegar. Sugar crystallizes. Put on medium heat until sugar melts. Remove from fire. Drain the fat from the pan on which the beef was fried, and heat it over very high heat. Scrape the sticky juice from the bottom of the pan and strain this liquid through a frequent sieve. Pour this liquid into a pan with the gastric sauce, warm and mix.

Cut the beef into thick slices and pour over the sauce.