Preheat the oven to 400°F. Line a 12-muffin tin with paper liners or spray with flour-based cooking spray.
In a large bowl, whisk together the flour, sugar, baking powder, salt, and cinnamon. Set aside.
In a medium bowl, whisk together the eggnog, sour cream, and melted butter until smooth.
Gradually stir the eggnog mixture into the flour mixture. Stir gently until just combined so the muffins stay soft.
Spoon the batter evenly into the muffin cups.
Bake for 18 minutes, or until a toothpick inserted into the center comes out clean.
Transfer the muffins to a cooling rack and cool completely.