Preparation

1. Preheat the oven to 350°F (175°C). Grease a 9×5 loaf pan and line it with parchment paper if desired.
2. In a large bowl, mix together the flour, baking soda, baking powder, salt, cinnamon, and nutmeg or pumpkin pie spice if using.
3. In another bowl, combine the pumpkin puree, eggs, oil (or melted butter), brown sugar, and sour cream (or Greek yogurt). Mix well until smooth.
4. Pour the wet ingredients into the dry ingredients and mix until just combined. Avoid overmixing.
5. In a separate bowl, beat together the softened cream cheese, sugar, and vanilla extract until smooth. Optionally add an egg yolk or spoonful of flour for a firmer swirl.

Baking

1. Add half of the pumpkin batter to the prepared loaf pan and spread it evenly.
2. Spoon the cream cheese filling over the batter in an even layer.
3. Add the remaining pumpkin batter on top and smooth it out.
4. Use a butter knife to gently swirl the layers together without overmixing.
5. Bake for 55 to 70 minutes, checking around 55 minutes for doneness. The loaf should spring back when lightly pressed, and a toothpick should come out with a few moist crumbs.
6. If the top browns too quickly, cover it loosely with foil.

Cooling

1. Let the bread cool in the pan for at least 10 minutes before transferring it to a wire rack. Allow it to cool completely for at least 1 hour before slicing.