Season a beef tenderloin, with salt and pepper, and leave it uncovered in the fridge for a couple of hours, so it releases moisture and the flavor concentrates. Seare on all sides in a pan with oil and butter.
Blend toasted bread, parsley, garlic, and butter into a dry dough. Roll it out between parchment paper and chill. If too moist, add more toasted bread or keep it in the mold with the parchment. If dry like a cracker, it will release easily and can go directly in the mold.
Slice seasonal mushrooms very thinly and sauté them with a bit of onion until you reach the right consistency. In the same pan, sauté Iberian bacon until nicely browned, then mix it in with a bit of chives.
Steam the endive leaves (or large spinach leaves) until fully cooked. Cut the parsley-garlic dough to fit a round mold. Place the steamed leaves inside, letting them hang over the edges to use as a lid. Add the tenderloin, then the mushroom mixture, and fold the leaves over to close it. Wrap with plastic wrap so it holds its shape and chill for at least an hour.
Cut two pieces of puff pastry, one for the base and a slightly larger one for the top. Remove the mold with the tenderloin, place it on the base, use egg yolk as "glue," and seal with the top piece.
Preheat the oven to about 200°C and bake for 20-30 minutes, monitoring with a thermometer until the inside reaches about 45°C. Turn off the oven and let it rest for 6-8 minutes.
Serve with a good homemade demi-glace.
