Sauté bacon in large skillet over medium heat until just crisp. Transfer to a paper towel-lined plate and reserve.
Add onion and shallot to skillet and sweat over medium heat, adding a little of the butter, if your bacon didn’t leave enough fat. Add garlic and cook another minute. Transfer with slotted spoon to a Dutch oven.
Season beef cubes lightly with salt and generously with pepper. Dredge in flour, shaking off excess. Add some butter to same skillet, as necessary, and brown meat on all sides, working in batches to avoid overcrowding. Transfer to Dutch oven as it is browned.
TURN OFF THE FLAME UNDER THE SKILLET. Pour Cognac (or brandy, which I used) into skillet. Holding skillet away from stove, turn on burner (I did the first part, but not the second, and the brandy caught fire impressively—see Kitchen Notes). Reduce by half. Stir in stock and 1/2 cup wine and bring to boil, scraping up any browned bits.
Stir in 2 tablespoons Dijon mustard and the whole grain mustard. Pour over beef and onion mixture in Dutch oven. Crumble/tear bacon into Dutch oven and stir to combine everything. Bring to simmer, cover partially, and cook about 2 hours. Add carrots and cook another 30 minutes.
Heat 3 tablespoons butter in a large skillet (perhaps the same one, which you washed while the beef and carrots were simmering) over medium high heat. Add mushrooms and cook, stirring frequently, until juice from the mushrooms cooks down and they begin to brown. Add remaining wine and remaining Dijon mustard and cook about 30 seconds. Stir mushroom mixture into stew and simmer another 10 minutes. Taste and adjust seasonings with salt, if needed.
Meanwhile, cook egg noodles. Divide egg noodles among 4 shallow bowls. Spoon stew over noodles and serve.