Preheat oven to 375°F. Place paper baking cups into muffin pan. Or use silicon muffin liners - I love them! Set aside.
In a medium bowl, whisk flour, pumpkin spice, baking soda and salt until well combined. Set aside.
In large bowl, mix together pumpkin, sugar and brown sugar.
Beat in eggs, vegetable oil and vanilla extract.
Slowly whisk in the flour mixture, until there are no lumps.
Fill muffin tins 3/4 full.
If using the cream cheese swirl: In a medium bowl, beat cream cheese until smooth. Add in sugar, egg yolk and vanilla extract and beat until well combined.
Top each muffin with about 1 tablespoon of cream cheese mixture and use a toothpick to swirl it into the batter.
Bake muffins for 18-20 minutes, or until a toothpick inserted in the center comes out clean.
Store in the fridge. Great warm or cold!
Notes
This makes about 18 regular size muffins. You can also make them as mini-muffins, which make them very easy to eat! They bake for about the same amount of time.