Preheat oven to 375 degrees Fahrenheit. Fill a muffin pan with paper liners and set aside.

In a large bowl, whisk together flour, baking soda, pumpkin pie spice, and salt. Set aside.

In a medium bowl, whisk together pumpkin, eggs, margarine, one and 1/2 cups sugar, and one teaspoon vanilla extract.

Add pumpkin mixture to the flour mixture and mix until just combined. Divide batter evenly among muffin cups, about 1/4 cup batter each.

In a small bowl, stir together cream cheese, egg yolk, remaining 1/4 cup sugar, and remaining 1/2 teaspoon vanilla extract until smooth. Dollop about one tablespoon cream cheese mixture onto the batter in each muffin cup and swirl gently with a toothpick.

Bake 18–22 minutes, until a toothpick inserted in the center comes out clean. Cool muffins in the pan for 10 minutes, then remove and serve warm or transfer to a wire rack to finish cooling.