1. Preheated the oven to 220 C/425 F/Gas Mark 7. Remove the mushroom stalks and arrange the mushrooms, rounded-side down, in a shallow baking dish.
2. Mix the butter, garlic, lemon juice and rind, parsley, salt and pepper together in a bowl. Divide the garlic butter between the mushroom cups.
3. Bake in the oven for 15-20 minutes, until the mushrooms are soft and the garlic butter is sizzling. Serve immediately with crusty bread.