01 - Preheat the oven to 400°F.
02 - Boil the potatoes in salted water until tender, about 15–20 minutes. Drain and return to the pot.
03 - Add milk, butter, salt, and white pepper to the potatoes. Mash until smooth and creamy. Set aside.
04 - Heat olive oil in a large skillet over medium heat. Sauté onion until translucent, about 3 minutes. Add garlic and cook for 1 minute.
05 - Add ground beef; cook, breaking up with a spoon, until browned and cooked through. Drain excess fat if needed.
06 - Stir in tomato paste, Worcestershire sauce, thyme, rosemary, salt, and pepper. Sprinkle flour over the meat and mix well.
07 - Pour in beef broth. Simmer for 3–4 minutes until slightly thickened.
08 - Stir in peas and corn. Remove from heat.
09 - Spread the beef mixture evenly in a 9x13-inch baking dish. Spoon mashed potatoes over the filling and spread evenly. Use a fork to create decorative ridges, if desired.
10 - Bake for 25–30 minutes, or until the top is golden brown.
11 - Let rest for 5–10 minutes before serving.