INGREDIENTS
1 x 28 oz bag frozen mashed potatoes (approx weight).
1 lb ground beef
1 onion, finely diced
salt
freshly ground black pepper
1 tbs Worcestershire sauce
1 tbs tomato ketchup
1 cups diced carrots (half inch dice)
1 cup frozen peas
1/2 cup beef broth (probably from paste concentrate)
2 oz grated cheese (Gruyère or Cheddar)
METHOD
Preheat the oven to 400F
Get over the fact you are using frozen mashed potatoes and start defrosting them in the microwave. Do not add liquid, no matter what the bag says.
In a large frying pan (ideally cast iron) sauté the ground beef until browned, remove with a slotted spoon into large casserole dish, leaving fat behind.
Discard all but 2 tbs of the fat, and sauté the onions in that remaining fat until lightly browned over medium heat.
Add the beef back to the pan, together with the salt, pepper, Worcestershire sauce and ketchup
Add the beef broth, peas and carrots. Cook over medium low heat until liquid mostly evaporates.
Decant the mixture into the baking dish
Season the mashed potatoes heavily with more salt and pepper.
Spread the potatoes evenly over the top of the meat mixture in the baking dish, roughing up the top with a fork to create peaks.
Sprinkle the grated cheese over the top and bake for 30 minutes. If the top is not golden brown, use the broiler on low to finish it.