Preheat the oven to 350°F (175°C). Grease a 9-inch square baking pan and line it with parchment paper.
In a medium bowl, whisk together flour, baking powder, baking soda, salt, cinnamon, and pumpkin pie spice.
In a large bowl, beat the softened butter, brown sugar, and granulated sugar until light and creamy.
Add the eggs one at a time, mixing well after each addition. Stir in the vanilla.
Mix in the pumpkin puree and sour cream until smooth.
Gradually add the dry ingredients to the wet mixture. Mix just until combined; do not overmix.
In a separate bowl, combine the chopped pecans, flour, brown sugar, cinnamon, and salt.
Stir in the melted butter until a crumbly topping forms.
Spread the pumpkin batter evenly into the prepared pan.
Sprinkle the pecan crumb mixture evenly over the batter.
Bake for 40–50 minutes, or until a toothpick inserted into the center comes out with a few moist crumbs.
Cool for at least 20 minutes before slicing and serving.