Preheat oven to 400 degrees.
Butter a 9 x 9 baking dish.
Bring a large pot of water to boil for potatoes.
In large skillet, brown beef and drain off excess fat.
Add carrots, onion, garlic and mushrooms to beef.
Saute for 5 minutes until veggies are tender.
Sprinkle beef mixture with flour and cook until flour is no longer visible.
Add beef stock, worcestershire, salt, pepper and nutmeg
Continue to cook until thick and bubbly. Turn off heat and mash potatoes.
For Potatoes
Drain potatoes and place back into large pot.
Add butter, sour cream, milk, salt and pepper.
Whip with electric mixer or use a hand masher (I use a hand masher).
Add more milk is thinner consistency is desired. A thicker mashed potato is recommended for this dish.
Pour beef mixture into baking dish. Top with mashed potatoes.
Bake for 30 minutes or until top is brown and sides of casserole are bubbly.
Cool for 10 minutes before serving.