Preheat the oven to 400 degrees F.
THEN PREPARE THE MEAT MIXTURE:
Then in a large skillet, add the ground beef and the onion. Brown the ground beef and break it apart with a wooden spoon or spatula. Cook until the beef is browned (approximately 5-6 minutes).
Drain off any excess grease.
Then add in the minced garlic. Cook for 1 minute.
Then stir in the flour and tomato paste. Stir well until these ingredients are well combined with the beef mixture.
Next add in the broth, frozen vegetables, Worcestershire sauce, onion powder, salt, pepper, Rosemary and thyme.
Bring this mixture to a boil and then reduce the heat to low to simmer for about 5 minutes.
THEN PREPARE THE MASHED POTATOES:
Place the potatoes in al large pot and cover them with water. Bring the water to a boil, reduce temperature to low to simmer and cook for 10-15 minutes until the potatoes are fork tender.
Drain the potatoes and then return to the potatoes to the hot pot.
Then add in the butter, milk, salt and pepper. Use an electric mixer to blend the potatoes until they are light and fluffy or use a hand masher to mash them to the consistency that you prefer.
THEN PREPARE THE CASSEROLE:
Spread the meat mixture on the bottom of the 9X13 baking pan.
Then spoon the mashed potatoes on top and spread it to make an even layer on top of the casserole.
Bake uncovered for 30-35 minutes until the casserole is cooked through and the top is slightly brown.
*You can broil for 2-3 minutes to brown the top of the potatoes if you prefer.
Then let the casserole set for 10-15 minutes. Serve and enjoy!