Preheat oven to 375°F.

In a large pot, boil potatoes until tender, about 15 minutes. Drain and mash with milk, butter, cheddar cheese, salt, and pepper.

In a skillet, heat olive oil over medium heat. Add onion and garlic, sauté until soft. Add ground beef and cook until browned.

Sprinkle flour over meat, stir in tomato paste, beef broth, and Worcestershire sauce. Bring to a simmer and let thicken, about 5 minutes.

Stir in frozen vegetables and cook for another 5 minutes. Remove from heat.

In a baking dish, spread the meat mixture evenly. Top with mashed potatoes, spreading to the edges to seal.

Bake for 20 minutes or until the potatoes are golden. Let stand for 10 minutes before serving.