How to Make It
Make the streusel: Heat oven to 350° F. Combine the pecans, butter, brown sugar, cinnamon, pumpkin pie spice, and salt in a medium bowl until well combined; set aside.
Make the cake: Butter a 12-cup Bundt pan and dust with flour, tapping out the excess. Whisk together the flour, baking powder, baking soda, and salt in a medium bowl; set aside.
Beat the butter, granulated sugar, and brown sugar with an electric mixer on medium-high until light and fluffy, 2 to 3 minutes. Beat in the eggs and vanilla, scraping down the sides twice. Reduce mixer speed to low and add the flour mixture and sour cream in alternate additions, mixing well between additions and ending with the flour mixture. Spread half the batter in the pan and top with half the streusel; repeat.
Bake, rotating once, until golden brown and a toothpick inserted in the center comes out clean, 45 to 50 minutes. Cool for 10 minutes in the pan. Invert onto a wire rack to cool completely. Wrap and store for up to 2 days at room temperature (or freeze for up to 2 weeks).