01 - Preheat oven to 400°F.
02 - Place potatoes in a large pot of salted water. Bring to a boil and cook until tender, about 15 minutes. Drain well.
03 - While potatoes cook, heat oil in a large skillet over medium heat. Add onion and carrots, sauté for 4–5 minutes until softened.
04 - Add garlic and cook 1 minute. Add ground beef, breaking it up with a spoon, and cook until browned and no longer pink.
05 - Stir in tomato paste, cook 1 minute. Add beef broth, Worcestershire sauce, thyme, salt, and pepper. Simmer 5 minutes. Stir in peas, cook 2 more minutes. Remove from heat.
06 - Mash the drained potatoes with butter, milk, salt, and pepper until smooth and creamy.
07 - Spread the beef mixture evenly in a 2-quart baking dish. Top with mashed potatoes, spreading to cover the filling completely.
08 - Use a fork to create ridges on the surface. Bake for 20 minutes or until the top is lightly golden and filling is bubbling.
09 - Let stand 5 minutes before serving.