Toss beef cubes with flour, salt, and pepper.
In a stockpot over high heat, melt butter then quickly sear the beef. Don’t cook all the way through, just sear the outside, about 1 minute.
Remove beef from heat and set aside.
Add the oil and onions. Reduce heat to medium and stir often until softened. Add garlic, and let it cook for about 30 minutes, stirring.
If you are going to use a crockpot, this is the point where you would transfer all ingredients, (including seared beef) other than the frozen peas, to the crockpot and cook on low, 3-4 hours until tender. Add peas at the end. Or if continuing on the stove, add the carrots, celery, potatoes, seared beef, crushed tomatoes, beef broth, bay leaves, and Italian seasoning. Mix to combine. Cover and cook on low 2-3 hours until vegetables and beef are tender. Don’t crank up the heat or the meat will be tough! If the meat isn’t fall-apart tender, it needs more time.
Add the frozen peas and Worcestershire sauce, stir to combine, and let cook a few more minutes. Taste and season with more salt and pepper if needed.
Serve hot and refrigerate any leftovers.