Prepare the apple rings: In a large bowl, combine the sliced apple rings and granulated sugar. Let it sit for about 15 minutes, until the apples start to release their juice and the sugar is dissolved.
Prepare the batter: In a separate bowl, whisk together the flour, cinnamon, nutmeg, and salt. Gradually add the buttermilk to the dry ingredients and mix until a smooth batter forms.
Dredge the apple rings: Dredge the apple rings in the batter, making sure they are fully coated.
Fry the apple rings: Heat about 2-3 inches of vegetable oil in a deep frying pan over medium-high heat. When the oil is hot, add a few of the battered apple rings to the pan (do not overcrowd). Fry for about 2-3 minutes on each side, until the apple rings are golden brown and crispy.
Drain and dust: Remove the fried apple rings from the oil and place them on a paper towel-lined plate to drain excess oil. Dust the apple rings with cinnamon sugar (if using).
Serve: Serve the Fried Cinnamon Apple Rings warm and enjoy!