Peel and chop russet potatoes into even-sized pieces. Boil in salted water for about 15 minutes until fork-tender. Drain and mash with butter, milk, garlic powder, salt, and pepper. Allow to cool slightly.

In a large skillet, heat olive oil over medium heat. Add diced onion and minced garlic, sauté until translucent. Brown ground beef, then add tomato paste, Worcestershire sauce, mixed vegetables, beef broth, salt, and pepper. Simmer for 5-7 minutes until thickened.

Spread the beef mixture into a 9x9 baking dish. Pipe mashed potato mixture over the meat to form ghost shapes. Use peppercorns or olives for spooky eyes.

Preheat oven to 375°F (190°C). Bake the assembled pie for 20-25 minutes until lightly golden and bubbling.