The night before place the goose pieces, onion, carrot, celery, bouquet garni, and red wine into a large bowl. Cover with plastic and refrigerate overnight. The next day, remove the goose pieces from the marinade and dry on paper towels. Strain the marinade into a bowl. In an ovenproof casserole or Dutch oven, over a moderate heat, brown the goose pieces without the addition of any fat. Drain on paper towels. Pour off any rendered fat from the casserole. Add the butter to the casserole and melt. Whisk the flour and cook for 2 minutes, whisking constantly. Add the reserved marinade, little by little. Return the goose pieces to the casserole and bring to a boil. Reduce the heat, cover, and simmer for 1 1/2 hours. Dry off the mushrooms and thinly slice them horizontally. Heat the olive oil in a frying pan and sautÄ the mushrooms. Five minutes before serving, stir the mushrooms into the stew. Serve with grilled or fried pieces of bread.
