Prepare the Mashed Potatoes:

1. Place the peeled and quartered potatoes in a large pot and cover with water. Add a pinch of salt.
2. Bring to a boil, then reduce heat and simmer for about 20 minutes, or until the potatoes are tender.
3. Drain the potatoes and return them to the pot.
4. Add the milk and butter, then mash until smooth and creamy. Season with salt and pepper to taste. Cover and keep warm.

Cook the Ground Beef and Prepare the Gravy:

1. In a large skillet, brown the ground beef over medium-high heat until no longer pink. Drain any excess fat.
2. Add the diced onion and minced garlic to the skillet with the beef. Cook until the onions are translucent, about 5 minutes.
3. Sprinkle the flour over the beef mixture and stir to combine. Cook for 1-2 minutes to remove the raw flour taste.
4. Gradually pour in the beef broth, stirring constantly to avoid lumps.
5. Add the Worcestershire sauce and season with salt and pepper.
6. If using, stir in the frozen peas and carrots. Simmer for 5-7 minutes, or until the gravy thickens and the vegetables are heated through.