Kohlrabi-Topped Shepherd's Pie

1. 1Heat the oven to 425°F and arrange a rack in the upper third.
2. 2Trim the stem ends and any stalks or greens from the kohlrabies. Using a vegetable peeler, peel the skin and fibrous inner layer until you reach the white flesh. Cut the flesh into 1-inch cubes and place in a large bowl.
3. 3Add the oil, salt, and pepper and toss to combine. Transfer to a baking sheet and arrange in an even layer. Roast until knife tender, about 30 minutes. Meanwhile, make the filling.

For the filling:

1. 1Heat the oil in a large heavy-bottomed pot or Dutch oven over medium-high heat until shimmering. Add the lamb, 1 teaspoon of the salt, and the measured pepper. Cook, using a wooden spoon to break up the lamb into small pieces, until the meat is completely cooked through and most of the moisture has evaporated, about 7 to 10 minutes. Remove with a slotted spoon to a medium bowl; set aside.
2. 2Reduce the heat to medium. Add the carrots, onion, garlic, thyme, and remaining 1/2 teaspoon of salt to the pot. Season with pepper and cook, stirring occasionally, until the vegetables are softened and starting to brown, about 4 minutes. Return the lamb and any accumulated juices to the pot.
3. 3Add the tomato paste and stir to coat the lamb and vegetables. Cook, stirring occasionally, until the tomato paste is no longer raw-tasting, about 2 minutes. Add the wine and cook, stirring occasionally, until it has completely evaporated, about 1 minute. Sprinkle in the flour and cook, stirring occasionally, until it’s no longer raw-tasting, about 1 minute.
4. 4Add the beef broth and Worcestershire, scrape up any browned bits that have accumulated on the bottom of the pot, and bring to a boil. Reduce the heat to medium low and simmer, stirring occasionally, until the filling has thickened, the liquid is reduced by half, and the flavors have melded, about 20 minutes. Taste and season with additional salt and pepper as needed; keep warm.

To finish the topping and assemble:

1. 1Place the roasted kohlrabi in the bowl of a food processor fitted with a blade attachment. Add the butter and process until smooth, about 2 minutes. Taste and season with salt and pepper as needed. Add the egg yolks and process until just incorporated; set aside.
2. 2Add the peas to the filling and stir to combine. Transfer the filling to a 13-by-9-inch baking dish and spread it into an even layer.
3. 3Drop the kohlrabi topping in large spoonfuls over the filling and spread it into an even layer. Bake until the shepherd’s pie is bubbling and starting to brown around the edges, about 25 minutes. Remove the dish to a wire rack and let it sit for 5 minutes before serving.