1/4 pound salt pork, diced
1 large onion, finely diced
3 shallots, chopped
2 to 4 tablespoons unsalted butter
2 pounds beef chuck, in 1-inch cubes
2 tablespoons all-purpose flour
Kosher salt and black pepper
1/2 cup Cognac
2 cups beef stock
1/2 cup Dijon mustard
4 tablespoons Pommery mustard or other whole-grain Dijon mustard
4 large carrots, peeled and cut into half-moon slices
1/2 pound mushrooms, stemmed, cleaned and quartered
1/4 cup red wine
Place salt pork in a Dutch oven over low heat, and cook until fat is rendered. Remove solid pieces with a slotted spoon, and discard. Raise heat, and add onion and shallots. Cook until softened but not browned, 10 to 15 minutes. Use a slotted spoon to transfer to a large bowl.
If necessary, add 2 tablespoons butter to the pot to augment fat. Dust beef cubes with flour, and season with salt and pepper. Shake off excess flour, and place half the cubes in the pot. Cook over medium-high heat until well browned, almost crusty, on all sides, then transfer to a bowl with onions. Repeat with remaining beef.
Add Cognac to the empty pot, and cook, stirring, until the bottom is deglazed and the crust comes loose. Add stock, Dijon mustard and 1 tablespoon Pommery mustard. Whisk to blend, then return meat and onion mixture to pot. Lower heat, partly cover, and simmer gently until meat is very tender, about 1 1/2 hours.
Add carrots, and continue simmering for 30 minutes, or until slices are tender. As they cook, heat 2 tablespoons butter in a medium skillet over medium-high, and sauté mushrooms until browned.
Stir mushrooms into stew along with remaining mustard and red wine. Simmer 5 minutes, then taste, and adjust seasoning. Serve hot.
For a slow-cooker version, render the salt pork in a large sauté pan, then sear the flour-dusted beef cubes in the fat. While the beef is browning, add onions, shallots, carrots, mushrooms and red wine to the slow cooker, along with the browned beef. Add Cognac to the empty pan, and deglaze. Add 1 cup stock (instead of 2), Dijon mustard and 1 tablespoon Pommery mustard. Transfer to the slow cooker. Cook on low for 6 to 8 hours. Add the remaining 3 tablespoons Pommery mustard and warm through before serving.