Preheat oven to 350°F.
To make filling: Meanwhile, in a 12 inch oven safe skillet over medium high heat, cook together ground beef, onion, celery, red pepper and green pepper in bacon drippings or olive oil. Cook for 8-10 minutes or just until no pink remains in beef. Drain excess fat from pan.
To the beef, add peas and carrots, minced garlic, garlic salt, lemon pepper, Italian, seasoning, thyme and garlic. Stir and cook for 1 minute.
To the skillet add beef broth, Worcestershire sauce and tomato paste. Lower heat to simmer, stirring just until tomato paste has melted and sauce slightly thickened. Remove from heat.
To make topping: Cover potatoes with cold water, season with 1 teaspoon salt. Bring to a boil, boiling for 8-10 minutes or until fork tender. Drain well. Add butter, milk, sour cream and reserved salt, whipping with an electric mixer until smooth. Add additional milk as needed to thin. Taste and adjust salt to taste. (This can be done up to 2 days in advance and chilled until assembling.)
Spread the top with mashed potatoes, dot with pats of butter and sprinkle with Parmesan cheese.
Bake for 30 minutes until bubbly around the edge. May broil the top if desired to brown further.
Let stand for 5 minutes then serve garnished with fresh parsley.