Thinly slice the mushrooms. On a hot grill (or grill pan), fry the mushrooms until they start to show grill marks. Arrange on the bread. Top with a little Castello Traditional Danish Blue and quickly grill in the oven until the cheese is slightly melted. Finish with fresh rosemary and olive oil.
To get the best result, use day-old bread in thin slices and then either toast them, fry them in oil or pop them on the grill. If you love garlic, rub the toasted bread with a clove of garlic. A couple of rubs is enough to get some garlicky flavour without it being too overpowering.