1. Place the bacon in a dutch oven over medium-low heat and cook until the fat is rendered. Remove the solid pieces with a slotted spoon and discard. Raise the heat, add the onion and shallots, and cook until softened but not brown, 10to 15 minutes. Use a slotted spoon to transfer to a large bowl.
2. If necessary, add 2 tablespoons butter to the pot to augment the fat and increase the heat to medium-high. Dust the beef cubes with the flour and season with salt and pepper. Shake off any excess flour and place half the cubes in the pot. Cook until well browned, almost crusty, on all sides, then transfer to the bowl with the onions. Repeat with the remaining beef.
3. Add the cognac to pot, and cook, stirring, until the bottom is deglazed and the crust comes loose. Add the broth, dijon mustard, and 1 tablespoon Pommery mustard and whisk to blend, then return the meat and onion mixture to the pot. Lower the heat, partially cover the pot, and simmer gently until the meat is very tender, about 1-1/2 hours.
4. Add the carrots and continue simmering for 30 minutes, or until tender.
5. Meanwhile, melt 2 tablespoons butter in a meduim skillet over medium-high heat, and saute the mushrooms until browned and tender.
6. Stir the mushrooms into the stew, along with the remaining 3 tablespoons Pommery mustarde and the red wine. Simmer for 5 minutes, then taste and adjust the seasoning.
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