Preheat oven to 350ºF
Set a large Dutch oven over medium heat. Add pancetta (or bacon) and cook for 10 minutes, until fat is rendered and pieces
are browned and crisp. Using a slotted spoon, transfer to a paper- towel-lined plate. Reserve the fat in the pan.
Increase heat to medium-high. Pat beef cubes dry, then season all sides with salt and pepper. Working in batches to avoid overcrowding, add enough beef to cover the bottom of the pot in a single layer. Sauté beef cubes until lightly seared on all sides and transfer to a large bowl. Repeat with the remaining beef.
Sprinkle flour over the cubed beef and toss.
Drain all but 1 tablespoon fat from the pot. Add carrots and onion to the pot and sauté for 7 minutes, or until beginning to brown. Add garlic and sauté another 1 minute. Stir in tomato paste and cook for 2 minutes, until darkened. Add a splash of wine, stirring to scrape up the browned bits, then add the rest.
Add 2 1/2 cups stock, 1 bay leaf, and thyme. Add pancetta, beef, and any juices. Season with 1/2 teaspoon salt and 1/4 teaspoon pepper. Bring liquid to a simmer, then cover and place in the oven. Cook for 3 hours, until meat is easily pierced