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.
Gradually stir the eggnog mixture into the flour mixture, just until combined.
Spoon the batter into the bottom of each paper-lined or sprayed muffin cup.
Bake 18 minutes, or until a toothpick inserted into the center comes out clean.
Transfer the muffins to a cooling rack to cool completely then serve.