Place sweet potato rounds in a large pot and cover with water. Bring to a boil and cook until tender (do not over-cook, they should still be slightly firm and not mushy). Drain and transfer to a large bowl.Add pecans, melted butter, brown sugar, white sugar, cinnamon, nutmeg, and salt to the bowl and stir to combine making sure potatoes are well-coated.Transfer mixture to a large casserole dish and bake at 400 for 15-20 minutes until sugars are dissolved and potatoes are very easily pierced with a fork. Stir the potatoes to coat with the sauce at the bottom of the dish and serve.