Sift the flour, baking powder, nutmeg and salt into a large bowl. Peel the sweet potato and mash it in a medium bowl until smooth. Break the eggs into a 2-cup measuring cup and gently whisk to break up the yolks. Add the milk and whisk to combine.
Add the milk mixture to the sweet potato puree and stir until blended then stir in the ¼ cup melted butter. Gradually stir the egg mixture into the dry ingredients just until incorporated, being careful not to over mix, which would develop too much gluten in the flour and make the pancakes tough. The batter will be a little bit thicker than traditional pancake batter, resulting in a creamier pancake. Let the batter rest for 10 minutes at room temperature.
Preheat an electric griddle to 300°F. Brush the griddle with butter. Spoon 1/4 cup of pancake batter onto the griddle for each pancake. Cook until bubbles start forming and the top of the pancakes starts to dry out, about 2 minutes. Flip the pancakes and cook another 2 minutes. This will take a bit longer than traditional pancakes due to the sweet potato. You want the pancakes to be a light golden brown and fully cooked through. Adjust your temperature on the griddle if the pancakes are browning too fast and are still gummy in the center.
Keep the pancakes warm in a low oven until ready to serve with the whipped cream and maple-cider syrup.
In a small saucepan, combine the maple syrup, cider, sherry vinegar, and cinnamon stick. Bring to a boil then reduce the heat to medium and cook until the mixture lightly coats the back of a metal spoon, 3-5 minutes. Remove from the heat.
Combine the cold whipping cream with the powdered sugar, cinnamon, and vanilla in the bowl of a stand mixer fitted with the whip attachment. Whip over medium low speed until the cream is rich and voluminous.