I just made these, and used rapeseed oil instead of the olive oil to roast them, and then olive oil instead of butter once they were done. I am very impressed. The mushrooms were, crunchy, smokey, and delicious. I can only imagine what they'd be like with butter. Only one negative point of note: the recipe directions aren't very clear about when to add the garlic and paprika, or even how to use it. I added both to the oil/pepper mixture to coat the mushrooms at the beginning but it would be nice if this was made clear. Great, simple recipe!