Classic Shepherd's Pie (or Cottage Pie, as it is known in some circles) marries a heavenly beef and vegetable stew with a savory potato mash, baking them together to perfection.
Brown ground beef in a large skillet. Remove from heat; drain beef in colander and set aside.
In the same large skillet, heat olive oil over medium heat. Add yams, onions, and carrots and cook, stirring frequently until everything is fork-tender; about 12-15 minutes.Add mushrooms and cook until mushrooms soften and release their juices; about 5 minutes. Remove from heat.
Sprinkle flour over everything, and then squirt in ketchup. Stir mixture to thoroughly coat everything. Return the pan to medium-low heat and cook, stirring constantly, for 1 or 2 minutes. Add the cream and cook another minute.
Add the beef broth, wine or grape juice, Worcestershire sauce, and thyme.Simmer over medium-low heat, stirring frequently, until mixture is thick but still saucy; 8-10 minutes.
Add the browned ground beef to the mixture in skillet and stir to combine. Pour the prepared beef vegetable mixture into a 1½- or 2-quart casserole dish.
Make the Topping
In a large saucepan over medium-high heat, bring potatoes, sweet potatoes, ½ teaspoon salt, and water to cover to boil. Reduce and simmer until tender, 15-20 minutes.Drain potatoes. Add butter and cream to potatoes and mash until smooth. Season with salt and pepper to taste.
Carefully spread prepared potatoes over meat and vegetable filling, using a spatula or large spoon to smooth the top.
Egg Wash (optional): In a small bowl, make an egg wash by whisking together 1 tablespoon water with egg. Brush the top of the potatoes with egg wash, and then drag a fork across the top to make ridges. Poke a 1-inch hole in the topping to allow the pie to vent as it cooks.
Bake it!
Adjust the oven rack to the middle position and preheat to 375°F | 190°C. Put the prepared pie in the oven and bake until the filling is hot and bubbling; about 20-30 minutes. Turn on the broiler and cook until top is golden brown, 2-4 minutes.Remove the pie from the oven and allow it to cool at least 10 minutes before serving.
Notes
This recipe can be prepared well ahead of time, and then baked from the refrigerator or freezer. How to bake Shepherd's Pie cold, from the fridge:Place the prepared pie on the middle rack in a cold oven.Set the oven temperature to 350°F | 176°C and bake until the center is piping hot; 45-60 minutes after the oven comes up to temperature.Turn on the broiler and cook until the top is golden brown, 2-4 minutes.Remove the pie from the oven and allow it to cool at least 10 minutes before serving.How to bake Shepherd's Pie frozen, from the freezer:Place the prepared pie on the middle rack in a cold oven.Set the temperature to 325°F | 160°C and bake until the center is piping hot; about 90 minutes after the oven comes up to temperature.Turn on the broiler and cook until the top is golden brown, 2-4 minutes.Remove the pie from the oven and allow it to cool at least 10 minutes before serving.