How to Make It
Preheat the oven to 350°. Butter a 9-by-13-inch glass baking dish. In a large skillet, melt the butter. Add the mushrooms and cook over moderate heat until their liquid evaporates, about 5 minutes. Raise the heat to moderately high and cook, stirring, until browned, about 3 minutes. Transfer the mushrooms to the prepared baking dish. Toss the bacon, parsley and pepper in the baking dish, then spread in an even layer.
In a large bowl, whisk the eggs well. Whisk in the cream, salt and a pinch of cayenne. Slowly pour the custard over the mushrooms and bacon and sprinkle the cheese over the top. Bake the custard for 50 minutes, or until just set. Transfer to a rack to cool for 15 minutes, then cut into squares and serve hot or warm.