Pat the beef pieces dry with paper towels, then season them generously with salt and freshly ground black pepper.
Optional: Heat the olive oil in a large skillet over medium-high heat. Sear the beef chunks for about 2–3 minutes on each side until nicely browned. Cook in batches if necessary to avoid overcrowding the pan.
Place the halved baby potatoes in the bottom of the slow cooker. Arrange the browned beef on top, and add the sliced onion and chopped carrots if using.
In a small bowl, melt the butter, then mix in the minced garlic, dried Italian herbs, crushed red pepper flakes (if desired), and chopped parsley.
Pour the beef broth evenly over the meat and potatoes. Drizzle the garlic butter mixture over everything and gently stir to coat the ingredients.
Cover and cook on LOW for 7–8 hours or HIGH for 4–5 hours, until the beef is tender enough to pull apart with a fork and the potatoes are soft but still hold their shape.
Taste the sauce and adjust the salt and pepper if needed. If the sauce seems too thin, leave the slow cooker uncovered for about 15 minutes, or mash a few potatoes into the broth to naturally thicken it.
Transfer the beef and potatoes to a serving dish, spoon the extra sauce over the top, garnish with fresh parsley, and serve warm.
