Peel and chop potatoes. Cook in a pot of salt water until tender, about 20 minutes. Drain water.

Add butter and milk to potatoes and mash together. Set aside.

Preheat oven to 350 F.

In a large pan crumble ground beef and add salt and pepper. Cook until meat is browned, then spoon into a bowl, retaining the grease in the pan. Set meat aside.

Drain off all but approximately 1 tablespoon of grease from the pan. Add onions, carrots, and garlic and cook until tender.

Stir in corn, peas, and beans, and cook 4-5 minutes.

In a separate pan, prepare gravy according to package directions. When gravy has thickened, add tomato paste and thyme.

Add gravy mixture and ground beef to vegetable mixture, and mix thoroughly.

Pour mixture into a 9 x 13 casserole dish. Spoon mashed potatoes on top and spread evenly.

Cover and bake 30 minutes. Remove cover and add cheese if desired. Bake an additional 10 minutes uncovered to lightly brown the potatoes or to melt the cheese if added.