Preheat oven to 375 degrees. Line muffin tin with liners, or spray generously with cooking spray.
Combine all dry ingredients in a large bowl. Whisk well.
Whisk together the egg, milk, sour cream, melted butter and pumpkin in a medium bowl until well combined.
Pour the wet ingredients into the bowl with the dry ingredients. Stir gently with a wooden spoon or spatula until just combined.
Scoop batter evenly into muffin cups until 3/4 full.
Baked 15 - 16 minutes until tops are beginning to brown and toothpick inserted in center comes out clean.