Cook the bacon under a preheated medium broiler until golden brown on both sides.
Meanwhile, quarter or slice the mushrooms if they are large.
Melt the butter in a frying pan, add the mushrooms and fry until wilted, stirring occasionally.
Continue cooking until the liquid exuded from the mushrooms has evaporated and they are golden brown.
Arrange the bacon and mushrooms in a warmed serving dish and serve hot.