Heat the oven to 350°F (175°C). Grease a 9x5-inch loaf pan and line it with parchment paper, leaving an overhang on the long sides for easy lifting.
Make the streusel: in a small bowl, rub the flour, brown sugar, cinnamon, and cold butter together with your fingertips until crumbly, then stir in the chopped pecans. Set aside.
Make the cream cheese swirl: beat the softened cream cheese, sugar, egg yolk, vanilla, and flour until completely smooth and creamy, with no lumps. Set aside.
Whisk the dry ingredients: in a medium bowl, whisk the flour, baking soda, salt, cinnamon, pumpkin pie spice, and nutmeg.
Mix the wet ingredients: in a large bowl, whisk the granulated sugar, brown sugar, eggs, pumpkin puree, oil, sour cream, and vanilla until smooth and glossy.
Combine: fold the dry ingredients into the wet just until no dry streaks remain. Do not overmix, or the loaf will be tough.
Layer the loaf: spread half the pumpkin batter into the prepared pan and smooth the top. Spoon the cream cheese mixture over it and spread gently to the edges. Top with the remaining pumpkin batter and smooth the top.
Swirl: run a butter knife through the layers in a figure-eight pattern, 4 to 5 passes, to marble the cream cheese through the batter without fully mixing it in.
Top and bake: sprinkle the pecan streusel evenly over the top. Bake for 60 to 70 minutes, until a toothpick inserted into the pumpkin part (not the cream cheese) comes out with a few moist crumbs and the top is set and golden. Tent loosely with foil after 45 minutes if the top browns too fast.
Cool completely: let the loaf cool in the pan for 15 minutes, then lift it out using the parchment overhang and cool completely on a wire rack, at least 1 hour, before slicing — the cream cheese center needs time to set.