In the 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 the 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, then stir in the Calva