1 (18.25 ounce) package white cake mix
1 cup vegetable oil
1 cup white sugar
2 tablespoons distilled white vinegar
3 eggs
1 cup milk
2 teaspoons vanilla extract
1 cup chopped pecans
4 cups buttermilk
Preheat oven to 350 degrees F (175 degrees C). Grease and flour a 9 inch cast iron skillet. In a large bowl, combine cake mix, oil, sugar, vinegar, eggs, milk and vanilla extract. Mix until smooth and pour mixture into prepared pan.
Bake in preheated oven for 85 to 90 minutes, or until a toothpick inserted into the center of the cake comes out clean. Cool cake completely, about 40 minutes. Cool completely in pan. Chill in refrigerator or overnight.