Heat 1 tablespoon of the oil in a hot frying pan and add the beef. Stir over high heat until golden brown. Using a metal colander, carefully drain any fat or liquid from the meat and return it to the pan. Sprinkle the flour over the meat and coat well. Cook for 1-2 minutes, stirring, until no raw flour is visible. Remove from the pan and set aside.
Lower the heat to medium, and heat the remaining oil in the same pan. Add the onions, celery, and carrots to the pan and fry until they begin to soften, about 5 minutes. Return the beef to the pan.
Add the stock and Worcestershire sauce to the pan stirring constantly to avoid any lumps.
Bring to a boil, then mix in the peas and parsley. Lower the heat to low, cover with a lid, and simmer for 30 minutes or until the mixture is tender. Taste and adjust seasoning with salt and pepper as needed.
While the filling cooks, prepare the mashed potatoes.
Cut the potatoes into evenly-sized chunks, about 1 to 2 inches thick. Place them in a large stockpot and add enough cold water to cover the potatoes by about 2 to 3 inches.
Add 1 tablespoon of salt to the water. Bring the water to a boil over high heat, then reduce the heat to medium-high (or whatever temperature is needed to maintain a steady boil). Continue cooking for about 10 to 15 minutes, or until a fork or knife can easily pierce the potatoes.
While the potatoes are cooking, gently heat the 8 tablespoons of butter, half-and-half, and milk in a separate pot. Warm the mixture until the butter is melted and the mixture is hot but not boiling.
Once the potatoes are cooked, carefully drain them and return them to the pot.
Add the butter and warmed milk mixture to the potatoes. Mash the potatoes using a ricer or potato masher, then gently stir with a wooden spoon or spatula to combine. The potatoes will gradually absorb the liquid and become creamy.
Adjust the consistency by adding more butter or half-and-half, if desired. Season with additional salt and freshly ground black pepper to taste.
Preheat the oven to 425°F/220°C.
Pour the beef mixture into a 3 to 3.5-quart casserole dish. Spoon the mashed potatoes on top and carefully spread them out in an even layer, covering the entire meat mixture. Run a spoon over the mixture to create texture that will crisp in the oven.
Bake in the oven for around 20 to 30 minutes or until the top is golden brown.
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Notes
Step-by-Step Guide
Check out the step-by-step photos just below the recipe card to guide you every step of the way! Detailed Instructions⬇️