Peel the potatoes and then use a mandoline to cut into thin discs. Cover a large plate with a sheet of cling film and layer the potato slices on top to make 6 individual layered potato rounds. Season with salt and then cover with a second sheet of cling film. Place in the microwave and cook for 2 minutes at 900W.
Cut 6 rounds out of the puff pastry. Clean and slice the mushrooms. Peel and thinly slice the shallots. Sauté the mushrooms in a frying pan with a dash of olive oil. Season with salt and cook for 2 minutes then add the shallots, white truffle oil and the port. Set aside once all of the liquid has evaporated.
Place a spoonful of mushrooms on top of each layered potato rounds and then cover with a pastry disc. Brush the edges with a little beaten egg yolk to seal.
Preheat the oven to 200°C.
Heat a frying pan and add a tiny amount of olive oil. Add the potato and mushroom tarts to the pan (potato side down) and cook until the potatoes are golden brown. Transfer to an ovenproof tray and cook for 20 minutes at 200°C.
Heat a frying pan to very hot and then cook the foie gras for 2 minutes on each side. Season well.
Serve the potato, mushroom and puff pastry tarts alongside the foie gras slices. Finish with a handful of fresh salad leaves dressed with white truffle scented olive oil.
«If you are pressed for time, prepare the layered potato discs in advance and then assemble the dish at the last moment.»