How to Make It
Preheat oven to 425°F. Roll out piecrust to 12 inches in diameter. Press into a (10-inch) pie plate; crimp edges. Prick all over with a fork. Chill until ready to use.
Heat 2 tablespoons of the butter and 1 tablespoon of the oil in a large skillet over medium-high. Add onions, and cook, stirring often, until softened and lightly browned, about 8 minutes. Reduce heat to medium, and cook, stirring occasionally, until golden brown, about 20 minutes. Add brandy; cook until slightly reduced, scraping up browned bits, about 30 seconds. Transfer onion mixture to a bowl.
Prepare roast according to package directions. Drain jus into a large liquid measuring cup. Add consommé to jus; set aside.
Heat remaining 1 tablespoon each butter and oil in a large nonstick skillet over medium-high. Add mushrooms and carrots to skillet, and cook until browned and tender, about 7 minutes. Add thyme, and cook until fragrant, about 1 minute. Stir in flour, and cook until toasted, about 1 minute. Pour in reserved jus mixture, and cook, stirring often, until thickened, about 3 minutes. Stir in onion mixture, all accumulated juices, roast, and salt.
Remove prepared piecrust from refrigerator, and place in preheated oven. Bake until lightly browned, about 15 minutes. Remove from oven. Fill crust with beef-onion mixture. Place bread pieces evenly over top. Sprinkle evenly with Gruyère. Bake at 425°F until top is golden, filling is bubbly, and cheese is melted, about 15 minutes. Remove from oven, and let stand 5 to 10 minutes before serving. Sprinkle with chives. Serve hot.