Preheat the oven to 400°F (200°C).

In a large pot, add the diced potatoes and cover with water. Bring to a boil and cook until tender, about 15 minutes. Drain the potatoes and return them to the pot.

In a skillet, cook the ground beef over medium heat until browned. Add the chopped onion and diced carrots. Cook until the vegetables are tender, about 5 minutes. Stir in the frozen peas.

In a small bowl, whisk together the beef broth, Worcestershire sauce, flour, 1 tablespoon of butter, salt, and black pepper. Pour the mixture into the skillet with the ground beef and vegetables. Cook until thickened, about 5 minutes.

Mash the cooked potatoes with the remaining 1 tablespoon of butter. Season with salt and black pepper to taste.

Transfer the ground beef mixture to a baking dish. Spread the mashed potatoes evenly over the top. Bake for 20 minutes, or until the potatoes are golden brown.