Heat olive oil in a large Dutch oven over medium-high heat. Brown the cubed beef on all sides for 8-10 minutes total, working in batches to avoid crowding the pan and ensuring proper caramelization for deep flavor.
Remove beef and set aside, then sauté diced onion and minced garlic in the same pot for 3-4 minutes until fragrant and softened. Stir in tomato paste and cook for 1 minute to deepen its color and concentrate flavors.
Return beef to the pot and pour in beef broth, scraping up all browned bits from the bottom. Add bay leaf, thyme, rosemary, salt, and pepper, then bring to a simmer.
Cover and reduce heat to low, simmering for 25 minutes until beef begins to tenderize. This hearty beef casserole crowd favorite develops its signature depth during this crucial braising phase when flavors meld together beautifully.
Add diced potatoes, carrots, and celery to the pot and continue simmering covered for another 15-20 minutes until vegetables are nearly tender. The hearty casserole should smell amazing at this point.
In a small bowl, whisk cornstarch with water to create a slurry. Stir this into the bubbling beef casserole to thicken the sauce, cooking for 2 minutes until it coats the back of a spoon.
Remove bay leaf and stir in frozen peas, cooking for 3-4 minutes until heated through. Taste and adjust seasoning as needed before serving your crowd comfort creation.