1. In a medium-sized pot, place the potatoes, which should have been peeled and quartered. Cover the potatoes with a layer of cold water at least an inch thick. Put a teaspoon of salt into the mixture. Allow the potatoes to boil, then reduce to low heat and cook until the potatoes are soft (this should take about 20 minutes).
2. Set the oven to 400 degrees Fahrenheit and leave it to heat up.
3. Melt four tablespoons of butter in a large sauté skillet over medium heat while the potatoes are cooking. Pour in the chopped onions and cook, occasionally stirring, until the onions are soft; this should take about 6 to 10 minutes.
4. If you’re using them, vegetables should be added as per their cooking time. Carrots should be cooked alongside onions because they take the same time to cook as onions.
5. If using peas or corn, add them near the end of the onion cooking time or after the meat begins to cook, as these ingredients typically take very little time to cook.
6. Combine the ground beef, onions, and veggies and add them to the contents of the pan. Cook until the meat is no longer pink. If necessary, drain any extra fat from the pan (if the fat content is more than one tablespoon). Add salt and pepper to taste.
7. Pour in the Worcestershire sauce and beef broth into the pan. It would help reduce the heat to low and let the broth simmer at this cooking stage. Cook for 10 minutes, uncovered, adding more beef broth as needed to prevent the meat from losing all its moisture.
8. Taste the cooked filling and season with additional salt, pepper, Worcestershire sauce, or other ingredients as desired.
9. Remove the potatoes from the pot when they are done cooking (a fork should easily pierce them) and set them in a dish with four tablespoons of butter. Taste and season with salt and pepper after mashing with a potato masher or fork.
10. In a large baking sheet (such as a 9 x 13-inch casserole), spread the cooked mixture out equally.
11. On top of the ground meat, spread the mashed potatoes. With a fork, scuff up the surface of the mashed potatoes to create peaks that will brown nicely. You may also make creative patterns in the mashed potatoes using a fork if you want.
12. Place the baking pan in a 400°F oven and leave it for 30 minutes, or until its contents are browned and bubbling. If necessary, broil the mashed potatoes for the last few minutes to brown the surface.
13. (Take care when broiling in Pyrex or glass dishes; the strong heat of the broiler has been known to fracture them.) This shouldn’t be an issue if you’re using a metal or ceramic or casserole dish.)
14. Your shepherd pie is ready to be served.

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