Pat the beef cubes dry with paper towels and season with salt and black pepper.
Heat olive oil in a large skillet over medium-high heat. Add the beef cubes in batches and brown on all sides, about 3-4 minutes per batch. Transfer browned beef to the slow cooker.
In the same skillet, add chopped onion and minced garlic. Sauté for 2-3 minutes until softened and fragrant.
Stir in tomato paste and cook for 1 minute.
Sprinkle flour over the onion mixture and stir well to combine. Cook for another minute to remove the raw flour taste.
Slowly pour in the beef broth while stirring to avoid lumps, scraping up any browned bits from the skillet.
Add Worcestershire sauce, dried thyme, and dried rosemary. Stir to combine and bring the mixture to a simmer for 2-3 minutes.
Pour the broth mixture over the beef in the slow cooker.
Add the halved baby potatoes to the slow cooker and gently stir to distribute evenly.
Cover and cook on low for 8 hours, or until the beef is tender and the potatoes are cooked through.
Before serving, taste and adjust seasoning with additional salt and pepper if needed.