You can also do this with a ciabatta!
Place the potatoes in a pre-heated oven at 200°C (about 45-60 minutes).
Melt the butter in a saucepan, add the garlic and mushrooms and cook gently for 5 – 10 minutes.
When the potatoes are cooked make a cross in the top, squeeze the base such that the top turns inside out. Pour the garlic and mushroom butter mixture in.
Top off with sour cream and herbs.