Cooking low and slow yields an even, tender piece of meat. In this recipe, it is cooked atop pieces of onion for flavor and aromatics.
Excerpted from Sheet Pan Paleo (Ulysses Press, 2016) by Pamela Ellgen.
Preheat the oven to 325 degrees F. Line a sheet pan with parchment paper.
Scatter the onion slices across the sheet pan, breaking them up to separate the rings from one another. Toss with 1 tablespoon of the oil to coat.
Rub the lamb leg with 1 tablespoon of the oil and then coat with the thyme, garlic, and lemon zest. Season generously with salt and pepper.
Place the meat atop the onion slices. Bake uncovered for 21⁄2 to 3 hours.
Cut the parsnips into 1⁄2-inch-thick spears. Toss with the remaining tablespoon of oil. Season generously with salt and pepper. In the final hour of cooking, place the parsnips atop the onion slices and return the pan to the oven.
Use an instant-read thermometer to gauge doneness on the meat: 125 degrees to 130 degrees F indicates medium rare, and 130 degrees to 135 degrees F indicates medium. Serve the lamb with the parsnips.