Place Steak Bites on a large plate. Pat dry with a clean paper towel.
Season generously with kosher salt and ground black pepper, set aside
Bring a 5.5qt Dutch Oven to medium-high heat. Add pancetta and move around the pan 1 minute. Reduce heat to medium and let fat render, about 3-5 minutes (moving the pancetta around every so often). Use a slotted spoon to remove the pancetta and place on a plate.
Turn heat back up to medium-high. In batches, sear both sides of the steak bites in the rendered fat. Remove from pan and set aside on a plate.
Add garlic and diced onion. Move around the pan until the garlic is fragrant and the onion softens, about 1 minute.
Add carrots and celery. Move around pan 1 minute.
Add 1/4 cup of the broth to deglaze the pan. Use a spatula to scrape up any bits from the bottom of the pan.
Add the remaining broth, beer, bay leaves, fresh thyme, tomato paste, worsteshire, potatoes, pancetta and steak bites (along with any juices that have settled on the plate).
Cover and let gently simmer 2-3 hours.
About 20 minutes before you are going to serve, add the onions and cover to let simmer.
Taste and add additional salt, as-needed (how much you need will depend upon what brand of broth you used, etc.).
Serve over mashed potatoes and enjoy!