Peel and cut potatoes; cook in salted water until tender, about 20 minutes, drain.
Add butter, milk and mash; set aside.
In large sauté pan add ground beef, salt, pepper and cook until browned. Transfer to casserole dish.
Drain off all but about 1 tbsp. fat from sauté pan, add onions, carrots and garlic and cook until tender.
Stir in beans, corn and peas. Cook for about 4-5 minutes (I usually add the beans and cook for a few minutes before adding peas and corn as they take a bit longer to cook.
In the meantime prepare gravy mix as per package instructions.
When gravy has thickened, stir in tomato paste and thyme.
Add gravy mix into vegetable mix, then stir in ground beef and pour into 2 quart casserole dish.
Top with mashed potato mix, cover and bake 350 degrees for 30 minutes.
(optional) Add shredded cheddar cheese and bake uncovered for an additional 10 minutes or until cheese is melted.