Despite its status as a classic comfort food, there’s nothing comforting about the many steps and piles of dirty dishes that shepherd’s pie usually requires. Using the cast-iron skillet as our sauteing, baking, and serving pan streamlined the process.
We used ground beef as our base and added tomato paste, garlic, and thyme to bump up the flavour. Flour, chicken broth, and Worcestershire sauce were all that we needed to create a rich gravy, and a final addition of green peas added a pop of freshness.
To give our potato topping necessary structure, we added milk, butter, and an egg. We used a zipper-lock bag to pipe the potato mixture on top of the pie and finished the dish under the broiler to give it an attractive golden crust. Don’t use ground beef that’s fattier than 93 per cent or the dish will be greasy.
Start to finish: 1 hour, 15 minutes
2 pounds russet potatoes, peeled and cut into 1-inch pieces
Salt and pepper
1/2 cup milk
1 large egg
4 tablespoons unsalted butter, melted, plus 2 tablespoons unsalted butter
2 carrots, peeled and chopped
1 onion, chopped fine
1 1/2 pounds of 93 per cent lean ground beef
2 tablespoons tomato paste
2 garlic cloves, minced
2 teaspoons minced fresh thyme or 1/2 teaspoon dried
2 tablespoons all-purpose flour
1 1/2 cups chicken broth
2 teaspoons Worcestershire sauce
1 cup frozen peas
Cover potatoes with water in large saucepan. Add 1 tablespoon salt, bring to simmer over medium-high heat, and cook until potatoes are tender, 8 to 10 minutes. Drain potatoes and return them to saucepan. Using potato masher, mash potatoes until smooth. Whisk milk and egg together, then stir into potatoes along with melted butter, 1 teaspoon salt, and 1/2 teaspoon pepper; cover and set aside.
Heat 10-inch cast-iron skillet over medium heat for 3 minutes. Melt remaining 2 tablespoons butter in skillet. Add carrots, onion, and 3/4 teaspoon salt and cook until softened, about 5 minutes. Add beef and cook, breaking up meat with wooden spoon, until no longer pink, 8 to 10 minutes.
Stir in tomato paste, garlic, and thyme and cook until fragrant, about 1 minute. Stir in flour and cook for 1 minute. Slowly stir in broth and Worcestershire, scraping up any browned bits and smoothing out any lumps. Bring to simmer and cook, stirring occasionally, until mixture has thickened slightly, about 10 minutes. Off heat, stir in peas and season with salt and pepper to taste.
Adjust oven rack 5 inches from broiler element and heat broiler. Transfer potato mixture to 1-gallon zipper-lock bag and snip off 1 corner to create 1-inch opening. Pipe mixture in even layer over filling. Smooth topping with back of spoon, then use tines of fork to make ridges on surface. Place skillet in rimmed baking sheet and broil until topping is golden brown and crusty, 5 to 10 minutes. Let casserole cool for 10 minutes before serving.