Heat the oven to 350°F (175°C). Arrange paper liners in a 12-well muffin pan.

Make the cream cheese filling: In a small bowl, beat the softened cream cheese, ¼ cup granulated sugar, egg yolk, and ½ teaspoon vanilla until smooth. Set aside.

Make the streusel: In a second bowl, stir together ½ cup flour, ¼ cup granulated sugar, ¼ cup brown sugar, and ½ teaspoon cinnamon. Cut the cold butter cubes into the mixture until coarse crumbs form. Stir in the walnuts or pecans if using, then refrigerate until ready.

Mix the dry ingredients: In a medium bowl, whisk the remaining 1 ¾ cups flour with the baking soda, baking powder, salt, pumpkin pie spice, cinnamon, ginger, and nutmeg.

Mix the wet ingredients: In a large bowl, whisk the granulated sugar, brown sugar, and oil together. Beat in the eggs one at a time, then blend in the pumpkin puree and vanilla extract.

Combine the mixtures: Pour the dry ingredients into the wet mixture and fold with a rubber spatula just until combined, leaving a few flour streaks if needed.

Assemble the muffins: Spoon batter into the lined cups halfway up. Drop one generous tablespoon of cream cheese filling into the center of each. Add another scoop of batter over the filling, filling each cup about three-quarters full. Sprinkle streusel over the tops and press lightly.

Bake for 20 to 22 minutes, or until a toothpick inserted in the muffin crumb away from the cream cheese comes out clean. Let cool in the pan for 5 minutes, then transfer to a wire rack.

Let the muffins rest for at least 15 minutes before serving so the cream cheese center can set.