Make half a batch of my homemade mashed potatoes to get 3 ½ cups. Set potatoes aside.
Preheat oven to 400 degrees F.
Add the oil to a large pan over medium-high heat. Add the ground beef to the pan and break it apart. Add the onions, parsley, rosemary, thyme, salt and pepper and stir well. Cook for 6-8 minutes, or until the meat is browned. Drain the grease.
Add the Worcestershire sauce and garlic and cook for about 1 minute, or until fragrant.
Add the flour and tomato paste and stir until well combined and no clumps of tomato paste remain.
Add the beef broth and frozen peas and carrots. Bring to a boil, then reduce to simmer. Simmer for 3-5 minutes, or until slightly thickened, stirring occasionally.
Pour the meat mixture into a 9×9 or 11×7 baking dish and spread evenly. Add the mashed potatoes to the top of the meat and spread evenly. Use a fork to “rake” lines into the mashed potatoes. Sprinkle the top of the casserole with the cheddar cheese, if using.
Bake for 15 minutes, then turn the broiler to high. Broil for about 5 minutes or until the potatoes and cheese are lightly browned on top. Keep a close eye on it, it can burn quickly.
Remove from heat and serve warm.
