Recipe Courtesy Anthony Bourdain, “Anthony Bourdain’s Les Halles Cookbook”
In a small pot, cook the bacon over medium-high heat until the meat is brown and the fat has been rendered, about 10 minutes, stirring occasionally to avoid sticking. Discard the fat and reserve the meat.
In a large pot, heat the butter until it foams. Add the shallot and cook until soft, about 3 minutes. Add the mushrooms and the apple and cook for 5 minutes. Add the bacon and then stir in the Calvados, scraping the bottom of the pot with the wooden spoon to dislodge any good brown stuff that might be clinging there. Stir in the cream and season with salt and pepper.
Once the mixture has come to a boil, add the mussels and cover. Cook for 10 minutes, or until all of the mussels have opened. Shake. Cook for another minute. Shake again. Serve immediately.