Generously season the roast beef with salt and pepper.
In a non-stick pan, brown the roast in oil on all sides over high heat. Remove from the heat and leave to cool on a rack.
Next, roughly chop the shallots and garlic. Add the mushrooms and chop again until everything resembles coarse breadcrumbs. Cook this mixture in a pan with a little butter. Continue cooking until the vegetation water has evaporated. Salt and pepper, let cool then set aside in the refrigerator.
On a floured work surface, roll out the puff pastry into a rectangle large enough to wrap around the roast.
Take the mushroom mixture out of the refrigerator and mix thoroughly with the liver pâté. Spread the roast with this mixture. Cut the black garlic cloves into thin slices and place them on top.
Place the roast on the puff pastry and fold it over to wrap it well. Cut off the excess dough and seal the ends well by pinching them. You can make decorations with the excess dough. Place them on the roast, wetting them slightly so that they stick to the dough.
EWrap the black garlic beef Wellington in cling film and refrigerate for at least 1 hour so that the puff pastry swells.
Preheat the oven to 220°c. Unwrap the black garlic beef Wellington and place it on a baking tray lined with parchment paper. Form a small chimney out of aluminum foil. Pierce the top of the dough using a knife and place the small chimney there.
Mix the egg yolk and the tablespoon of milk then brush the puff pastry with it. Bake for 10 minutes then lower the temperature to 200°c. Continue cooking for 20 minutes.
Let rest for 5 to 10 minutes before cutting and serving. There you go, your black garlic beef Wellington recipe is ready!