When fall finally cools things down, and sweaters are donned and the fires lit, this is the first dish I crave. The French have several versions and the English dozens, but whether you start with a hash of leftover roast or use ground lamb (or mutton when you can get it), mashed potatoes must top the lot or a shepherd's pie it ain't. As for the potatoes, we've included cooking them from scratch below, but if you have leftovers feel free to use them.Photo by Lynne Calamia
Heat oven to 400ºF with a rack in the middle position.
Peel the potatoes and cut in 1-inch chunks. Put in a 4-quart pot and add 1 tablespoon of the salt, and cover with cold water by 2 inches. Park over high heat, cover with a lid and bring to a boil, then uncover, lower the heat to maintain a simmer, and cook until tender, 8-10 minutes. Meanwhile, combine the half-and-half and butter in a microwave safe container and nuke until warmed through, about 35 seconds.
Drain the potatoes and return them to the pot. Mash with a potato masher then add the warm half-and-half mixture and 1 teaspoon of the salt. Continue mashing until smooth then stir in the egg yolk. Set aside.
Set a 12-inch cast iron skillet over medium-high heat and add the oil. When you see it shimmer (about 1.5 minutes), add the onion, carrots, and 1 teaspoon of the salt. Cook, stirring frequently, for 5 minutes, then stir in the garlic followed by the lamb, black pepper, curry powder, rosemary, thyme, and remaining salt. Stir, breaking up any clumps of meat with the back of a wooden spoon. Cook until the lamb is brown, about 5 minutes.
Sprinkle the flour over the lamb mix, then stir and cook for another minute. Stir in the tomato paste, chicken stock, and Worcestershire sauce. Bring to a boil, then decrease the heat to low, cover with a lid, and simmer, stirring occasionally, until the sauce is slightly thickened, about 10 minutes.
Kill the heat and stir in the peas. Then, spoon the mashed potatoes over the top of the meat mixture and smooth with an offset or silicone spatula. Move to the oven and bake for 30 minutes, until the top is golden brown. Cool for 15 minutes before scooping and serving.
Note: To reheat, I usually just spoon it into a bowl, cover loosely with a bit of plastic wrap and microwave on high until warmed through.