Heat the vegetable oil in a large skillet over medium-high heat.
Add the beef cubes in batches and brown on all sides, about 5 minutes per batch. Transfer browned beef to the slow cooker.
In the same skillet, add the sliced onion and cook for 3-4 minutes until softened.
Add the minced garlic and cook for 1 minute more, stirring frequently.
Transfer the onion and garlic to the slow cooker.
Add the carrots and parsnips to the slow cooker.
In a bowl, whisk together beef broth, tomato paste, Worcestershire sauce, dried thyme, dried rosemary, salt, and black pepper.
Pour the broth mixture over the ingredients in the slow cooker.
Add the bay leaf to the slow cooker and stir gently to combine.
Cover and cook on low for 6 hours or until the beef and vegetables are tender.
About 30 minutes before serving, preheat the oven to 400°F (200°C).
Remove the bay leaf from the slow cooker.
Transfer the hotpot mixture to a large ovenproof dish.
Arrange the sliced potatoes evenly over the top of the hotpot.
Brush the potatoes with melted butter and season with a little salt and pepper.
Bake in the preheated oven for 25-30 minutes or until the potatoes are golden and crispy.
Remove from the oven and let rest for 5 minutes before serving.