• Preheat oven to 200C / 400F / 180C fan forced.

First two steps below can be done at same time.

• Peel and chop potatoes into large chunks. Put them in cold water in saucepan. Bring to the boil and cook for 10 minutes. Drain. Mash and set aside.
• Bring another pan of water to the boil. Add 1/2 tablespoon of salt and then the pasta and boil for 10 minutes. Reserve 1/4 cup of the cooking water before draining the rest away. The pasta should not be cooked through.
• Heat oil in saucepan over medium heat. Add the onion and garlic and sauté for a couple of minutes until softened.
• Add the ham and thyme and sauté for a minute or so until the ham gets a little colour.
• Add the spinach and allow it to wilt a little before turning off the heat.
• Tip the cooked mixture into the bowl with the mashed sweet potato, then add the ricotta, nutmeg and salt and pepper to taste. Mix thoroughly.
• Pour the reserved pasta water into a 6 cup capacity casserole dish (or the same pan you cooked everything in as long as it is oven safe).
• Fill each shell with the filling and sit them side by side in the dish.
• Sprinkle over the cheese and a little more salt & pepper.
• Bake for 25 minutes or until golden on top.