Place a large saute pan over medium heat, add 2 tablespoons extra-virgin olive oil. Add sliced Vidalia onions and saute 12 to 15 minutes until softened and lightly caramelized.
While onions are cooking, peel and thinly slice the sweet potatoes.
Begin layering one-third of the sweet potatoes in a buttered 12-cup baking dish. Sprinkle potatoes with salt, nutmeg, cinnamon, and freshly ground black pepper. Add half of the onion mixture, then half of the shredded English cheddar. Repeat process. Top with remaining potatoes in a spiral and then with remaining cheese.
Mix 1 cup of heavy cream with 1 cup chicken stock in a large measuring cup and pour over potatoes. Cover with parchment and foil and put into oven for 30 minutes at 350 degrees Fahrenheit, then increase temperature to 425 degrees and cook 45 minutes more. Remove from oven and serve.