How to Make It
Preheat oven to 450°F.
Combine stock, flour, and pepper in a bowl. Heat oil in a large ovenproof skillet over high. Add beef; cook 5 minutes or until browned, stirring to crumble. Stir in thyme, garlic, and mushrooms; cook 3 minutes. Reduce heat to medium-high; cook 8 minutes or until mushrooms are browned. Stir in sherry, Worcestershire sauce, and salt; cook 1 minute. Add stock mixture; bring to a boil. Cook 4 minutes or until thickened. Stir in peas and onions.
Combine mashed potatoes and milk; spread over beef mixture. Bake at 450°F for 15 minutes. Turn on broiler (do not remove pan from oven). Broil 4 minutes or until lightly browned. Top with parsley.