Prick the potatoes with a fork in several places and place them on a baking tray lined with baking paper.
Bake them in the oven for about 1 hour until the flesh is fully cooked. Remove the potatoes from the oven and cut them in half lengthwise.
Scoop out the flesh, put it in a medium bowl and put the empty skins back on the baking tray for later.
Roughly mash the potatoes with 40 g butter, cream, Gorgonzola, 1 teaspoon of salt and a generous amount of freshly ground pepper and set aside.
Spread the remaining 10 g butter over the skins. Sprinkle the inside with salt and bake in the oven for 8 minutes until crispy. Remove from the oven and set aside.
Slice the mushrooms and chop the garlic and parsley.
Heat some butter and olive oil in a frying pan and fry the mushrooms until golden, add the garlic and parsley. Remove from the heat. Stir the mushrooms into the mashed potatoes and spoon the mixture into mounds in the potato skins.
Return the stuffed potatoes to the oven and cook until the top is crispy and golden brown.
Remove the stuffed potatoes from the oven, sprinkle with some walnuts and parsley, if you like, and serve.