How to Make It
Preheat the oven to 450°. On a baking sheet, bake the potatoes for about 1 hour, until tender.
Meanwhile, in a large skillet, melt 1 tablespoon of the butter in the olive oil. Cook the mushrooms over moderately high heat, stirring occasionally, until tender and golden, about 5 minutes. Season with salt and pepper.
Slice halfway down the length of each potato and spoon 1 tablespoon of butter and 2 tablespoons of cheese into each one. Season with salt. Top with the mushrooms and the remaining cheese. Bake for 3 minutes, until the cheese melts. Garnish with parsley and serve hot.