Preheat oven to 375F. Fill a muffin tin with paper liners and set aside.
In a large bowl, mix together the flour, baking soda, pumpkin pie spice, and salt. Set aside.
In a medium bowl, whisk together the pumpkin, eggs, margarine, 1 ½ cups of sugar, and 1 teaspoon of vanilla extract.
Add pumpkin mixture to the flour mixture and mix until combined. Divide the batter among the muffin cups, about ¼ cup ea.
, In a small bowl, stir together the cream cheese, egg yolk, remaining ¼ c sugar and remaining ½ teaspoon vanilla extract, until smooth. Dollop about 1 tablespoon of the cream cheese batter into each muffin tin and swirl gently with a toothpick.
Bake for 18-22 minutes, until a toothpick inserted in the center comes out clean. Cool muffins in the tin for 10 minutes, then remove and serve warm of transfer to a wire rack to finish cooling.