01 - Preheat oven to 400°F. Place potatoes in large pot, cover with cold salted water, bring to boil, then simmer 15-20 minutes until fork-tender.
02 - Heat olive oil in large skillet over medium heat. Add onion, cook 3-4 minutes until softened. Stir in garlic, cook 1 minute.
03 - Add ground beef to skillet, break apart while cooking until browned, 6-8 minutes. Drain excess fat if needed.
04 - Stir in tomato paste, Worcestershire sauce, thyme, rosemary, salt, and pepper. Cook 2 minutes to blend flavors.
05 - Pour in beef broth, simmer 5 minutes until mixture thickens slightly.
06 - Stir in frozen peas and corn, cook 2 minutes. Remove from heat.
07 - Drain cooked potatoes, return to pot. Add butter, milk, salt, and pepper. Mash until smooth and creamy.
08 - Spread beef mixture evenly in 9x13-inch baking dish. Spoon mashed potatoes over top in even layer. Sprinkle with cheddar cheese if desired.
09 - Bake 25 minutes until top is lightly golden and filling bubbles. Broil 2-3 minutes for crispier top if desired.
10 - Let cool 10 minutes before serving to allow layers to set.