There are many different ways to make this dish, and not just on St. Patrick's Day. In England and Ireland, shepherd's pie is always based on lamb (hence "shepherd"), while ground-beef versions are sometimes called cottage pie instead. At Solas, our authentic Irish pub in Boston, Mass., we serve both lamb and beef versions.
The recipe below calls for the pie to be baked in one large dish, in the traditional manner, but at the restaurant we the serve it in individual portions. We’ll heat up the cast-iron dishes to 400 degrees, add the ingredients, and then broil the top so a crust forms. That way, it arrives to our guests simmering hot.
Preheat an oven to 400 degrees.
Peel and quarter potatoes. Place in a pot and cover with 2 inches of water and season with salt. Bring to a boil and cook potatoes until tender, about 20 minutes.
While the potatoes are cooking, melt 4 tablespoons butter in large frying pan over medium heat.
Sauté onions in butter until tender, about 10 minutes. Add the carrots and cook until slightly tender, about 5 minutes.
Add ground beef and sauté until no longer pink, about 5-10 minutes. Add the peas and corn and continue to cook until they are cooked, about 5 minutes more.
Season with salt, pepper, and Worcestershire sauce.
Add half a cup of beef broth and cook, uncovered, over low heat for 10 minutes, adding more beef broth as necessary to keep moist.
In a large bowl, mash potatoes with the remaining butter, and season to taste.
Place beef mixture in a large 9-by-13-inch baking dish. Distribute mashed potatoes on top. Rough up with a fork so that there are peaks that will brown nicely. You can use the fork to make some designs in the potatoes as well, if you wish.
Bake until bubbling and brown, about 30 minutes. Broil for last few minutes, if necessary, to brown the top.