Heat oven to 350℉ (175℃)..
Spray three 6-inch cake pans with baking spray. Set aside.
In a medium bowl, whisk together flour, salt, baking soda, baking powder, pumpkin pie spice, and cocoa powder. Set aside.
In the bowl of a stand mixer fitted with the beater blade (flat beater for traditional stand mixers), beat butter and sugar until light and fluffy.
Add eggs, one at a time, beating well after each addition.
Add flour mixture alternately with buttermilk, beginning and ending with flour mixture, and stirring after each addition. Be careful not to over mix!
Stir in vanilla.
Evenly divide batter into prepared pans. If using a scale, it should be roughly 16.4 ounces per pan.
Bake about 30-35 minutes, or until cake tests done.