In a large Dutch oven or heavy-bottomed pot with a tightfitting lid, cook bacon/pancetta over medium-low heat until fat is rendered and lardons are browned and crisp, about 10 to 15 minutes. Transfer with a slotted spoon to a paper towel-lined plate. Reserve fat in pot.

Raise heat under pot to medium-high and cook until fat is starting to smoke. Lay half the beef cubes in a single layer in the pot. Cook until well browned on all sides, 10 to 15 minutes; transfer pieces to a plate as they brown. Repeat with remaining beef.

Reduce heat, if necessary, to prevent burning. Stir in onion, carrot and remaining ¼ teaspoon salt and cook until soft, about 10 minutes, stirring occasionally.

Stir in garlic, tomato paste, and Worcestershire sauce, and cook for 1 minute. Stir in flour, cook for 1 minute, then add wine, bay leaf and thyme, scraping up brown bits at bottom of pot. Bring to a boil.

Add browned beef and half the cooked lardons back to pot, cover, and transfer to oven. Let cook until beef is very tender, about 3 hours, turning meat halfway through. Ideally, cool and refrigerate until the next day. If not, procede to step 7.

On the next day remove some of the hardened fat on top, if desired. Mix.

In a medium skillet heat 1 tablespoon of butter over medium heat and sauté the mushrooms for 5 to 10 minutes. Add to the stew.

In the same skillet set over medium heat, combine pearl onions, remaining 1 tablespoon of butter, sugar, a pinch each of salt and pepper, and enough chicken stock or water to just cover the onions. Bring to a simmer and cook. The onions should be left with a nice shine to them. Set aside.