1 (18 ounce) package white cake mix
1 cup water
3 cups buttermilk
2 1/2 cups vegetable oil
1 3/4 cups pumpkin puree
1 1/4 cups water
1 tablespoon white sugar
1 teaspoon pumpkin pie spice
1 teaspoon vanilla extract
3 cups chopped pecans
Preheat oven to 350 degrees F (175 degrees C). Grease and flour two 9-inch round baking pans.
In a large bowl, mix cake mix, water, oil, pumpkin, water, sugar, pumpkin pie spice and vanilla. Stir gently with spoon. Pour batter into prepared pans.
Bake in the preheated oven for 45 minutes, or until a toothpick inserted into the center of the cake comes out clean. Allow to cool completely, then frost with pumpkin pecans.