Preheat the oven to 400º and place the rack in the center. 

First, peel the potatoes so you have them ready to go. If they’re big potatoes, cut them in quarters, but for most Yukon golds cut in half is fine. You want them to all be similar in size.

Next, prep the garlic and rosemary for the lamb. Instead of smashing the garlic, try keep each clove intact as you cut them into small slivers. Trim your rosemary into small pieces, as well. 

With a sharp knife, make tiny slits in the lamb and stuff them with garlic and then rosemary. You don’t need the whole lamb to be decorated this way–the fatty top layer should be good enough. If there are any obvious entry holes in the meaty sides of the lamb, feel free to push a couple of garlic slivers in there, too. 

Slice a few onion rings and place them in the bottom of a cast iron pot. Put your lamb on top, and coat with olive oil, making sure to cover all sides. 

Put the potatoes in next, and coat them with olive oil, too. Finish by placing a few raw onion rings on top. 

Optional: To add even more flavor, cut a few slices of lemon and place on top of the lamb. 

Sprinkle with salt and pepper, cover with a lid and bake for 10 minutes.

After 10 minutes, simply turn the oven down to 350º–no need to even open it. Let the roast cook for 40 minutes. 

After 40 minutes, remove the pot from the oven and take off the lid. Then place it back in the oven uncovered and bake for an additional 20 minutes. This last bit will give the top of the lamb and potatoes a little crispiness. (Don’t worry, not too much.)

When the cooking time is up, remove the roast and let it rest for at least 10-15 minutes before digging in. 

Serve with gravy or mint sauce.