Season beef cubes with salt and pepper and set side for 30 minutes to bring to room temperature.
In the meantime, in a large dutch oven or pot, saute the pancetta or bacon until crispy, and set aside on paper towel, leaving the fat behind.
Use the fat to saute the mushrooms until brown, then transfer to the plate with the rendered pancetta.
Add the pearl onions and brown on all sides, then set aside with the pancetta and mushrooms.
Preheat oven to 350 degrees F. Meanwhile, use the same Dutch oven to brown the beef cubes in batches, transferring each batch to a plate.
Be sure not to overcrowd the pan so that the beef browns nicely. If the pot needs more fat, add some olive oil.
Add the carrots and onion to the pot and saute for about 5 minutes. Stir in garlic and tomato paste and continue to stir for about 1 minute.
Add the beef back to the pot along with the thyme, bay leaf and red wine. Cover and transfer to the oven and cook for 1 1/2 hours, or until the beef is fork tender.
To serve, ladle stew into a bowl and scatter the top with rendered pancetta, pearl onions, mushrooms and a sprinkling of chopped parsley.