Hard-boil 2 eggs and let them cool. In a pan, fry the roundly sliced leeks for about 5 minutes. In another dish, mix the mince, breadcrumbs, 1 raw egg, chopped onion, salt and pepper. Mix it well until homogeneous. Peel the eggs and place them in the middle of the mince.
Form a loaf out of it. Onto a floured table, spread out the puff pastry. Make sure it is large enough to wrap the entire roll. Sprinkle the puff pastry with the braised leeks, smear the egg white from the remaining egg and wrap the mince inside to get a roll. Grease a tray well, place the roll in it and brush it with the last egg yolk and oil.
It's best to put the folded side of the roll facing down – to achieve a better visual effect. Place it in a preheated 356°F (180 °C) oven and bake for about 45 minutes. If necessary, cover the tray with foil for the last ten minutes.