01 - Preheat the oven to 400°F.
02 - In a large skillet over medium heat, brown the ground beef, breaking it apart with a spoon. Drain excess fat if necessary.
03 - Add the chopped onion and minced garlic to the skillet. Sauté for 2 to 3 minutes until the onion is translucent.
04 - Stir in tomato paste, Worcestershire sauce, dried thyme, salt, and black pepper. Mix thoroughly.
05 - Add frozen mixed vegetables and beef broth. Simmer for 5 to 7 minutes until the sauce has slightly thickened.
06 - Transfer the beef and vegetable mixture to an 8x8-inch baking dish.
07 - In a mixing bowl, blend mashed potatoes with butter and milk until smooth and creamy.
08 - Spread the mashed potato mixture evenly over the beef filling. Top with shredded cheddar cheese, if desired.
09 - Place the dish in the oven and bake for 20 minutes, until the top is golden brown and the filling is bubbling.
10 - Remove from oven and let rest for 5 minutes before serving.