Throughly grease a Bundt pan with shortening, being careful to grease all crevices.
Preheat the oven to 350 degrees and fit a standing mixer with a paddle attachement. Beat the butter and sugars on medium speed until creamy.
Add the eggs, one at a time, beating just until blended. Add in the pumpkin and vanilla and mix until everything is incorporated.
In a separate bowl, combine the flour, baking powder, baking soda, salt, and pumpkin pie spice. Set that near the standing mixer. In a separate container, measure out a cup of buttermilk.
Turn the mixer on low and add 1/4 of the flour mixture. Once it is incorporated, add in 1/3 of the buttermilk. Alternate adding the flour and buttermilk mixture, beating just until blended with each addition. Begin and end with the flour.
Remove the bowl from the mixer and use a spatula to scrape the sides and bottom. Pour in the chopped pecans and stir.
Spoon the batter into the Bundt pan and bake on the top oven rack for 50-60 minutes or until a kabob stick comes out clean.
Once slightly cooled, use a serrated knife to level off the top of the cake. Invert the Bundt pan onto a wire rack and let the Bundt cake completely cool upside down.