Heat bacon in an 8-qt. saucepan over medium-high heat; cook, stirring occasionally, until fat is rendered and bacon is crisp, 5–7 minutes. Using a slotted spoon, transfer bacon to a paper towel-lined plate; set aside. Season beef with salt and pepper. Working in batches, cook beef, turning as needed, until browned, 12–14 minutes. Transfer beef to a bowl; set aside. Add garlic, carrots, parsnips, and onion; cook, stirring occasionally, until slightly caramelized, 10–12 minutes. Add armagnac; cook, stirring and scraping up browned bits from bottom of pan, until reduced by half, 1–2 minutes. Add stock, wine, salt, and pepper; boil. Place parsley, thyme, bay leaves, and rosemary on a piece of cheesecloth; tie into a tight package and add to pan. Return beef to pan and reduce heat to medium-low; cook, covered slightly, until beef is very tender, 2–2 ½ hours. Uncover and stir in reserved bacon, plus chocolate, salt, and pepper; cook until chocolate is melted, about 5 minutes more. Keep stew warm.

Melt butter in a 12" skillet over medium-high heat. Add mushrooms; cook, stirring occasionally, until golden brown, 4–6 minutes. Season with salt and pepper, and stir into stew. Ladle stew into bowls; serve with bread on the side, if you like.