Roast Lamb with Potato, Onion & Pepper Gratin

This is a brilliantly designed one-dish meal: a bone-in leg of lamb roasts on a rack set directly over a layered gratin of potatoes, onions, and roasted red peppers in a large oval dish. As the lamb cooks, its juices drip down into the vegetables, basting them with rendered fat and meaty flavor.

The gratin builds up in layers, each seasoned with a mix of chopped garlic and fresh thyme. Thinly sliced baking potatoes go on the bottom (rubbed with a split garlic clove first), then sliced onions, then roasted red peppers. White wine and olive oil get poured over the whole stack before the lamb goes on top.

Turning the lamb every 15 minutes and basting with the liquid from the dish below keeps the meat moist on all sides and distributes the drippings evenly through the gratin. By the time the lamb hits rare at about 75 minutes, those potatoes on the bottom have soaked up wine, olive oil, garlic, thyme, and lamb jus.

Let the lamb rest on the rack after roasting so the last drippings fall into the gratin. Carve into thin slices and serve alongside scoops of the layered vegetables.

Pro Tips

• Slice potatoes and onions uniformly thin so they cook through in the same timeframe as the lamb
• Trim excess fat from the lamb but leave a thin layer. It renders and flavors the gratin as it cooks
• A sturdy oven-safe cooling rack works perfectly as the roasting rack over the gratin dish
• For medium-rare lamb, use an instant-read thermometer and pull at 130 degrees internal

Variations

• Rosemary version: Swap the thyme for fresh rosemary and add a squeeze of lemon juice to the gratin for a more classic Provencal flavor
• Root vegetable gratin: Layer parsnips and sweet potatoes alongside the regular potatoes for a more complex base