Step 1: Season the beef cubes with salt and pepper, then toss with flour to coat lightly.
Step 2: Heat olive oil in a large skillet over medium-high heat. Brown the beef in batches, about 3-4 minutes per batch, then transfer to the crockpot.
Step 3: In the same skillet, sauté onion, carrots, and celery for 5 minutes until softened. Add garlic and cook for 1 more minute.
Step 4: Transfer the vegetables to the crockpot. Add potatoes, beef broth, red wine (if using), tomato paste, thyme, rosemary, and bay leaf.
Step 5: Stir everything together, cover, and cook on low for 8 hours or high for 4 hours, until beef is tender.
Step 6: Remove bay leaf, adjust seasoning with salt and pepper, and serve hot.