Preheat the oven to 350 degrees, grease and flour three 8x2 inch round pans (you could also use two 9 inch pans)
In a medium bowl, whisk the flour, baking powder, baking soda, cinnamon, nutmeg and salt. Set Aside
In another bowl, add the sweet potatoes, milk and vanilla. Set Aside.
In the bowl of your mixer, add the butter and mix at medium speed until smooth. Gradually add the sugar and continue to mix on medium speed for 3 to 5 minutes until lightened in color and fluffy.
Mix in the oil. Add the eggs one at a time, mixing until the yellow of the yolk disappears.
WIth the mixer on low speed, alternately add the flour mixture and milk mixture, beginning and ending with the dry ingredients (3 additions of dry ingredients and 2 of the milk/sweet potato mixture).
Do not mix above medium speed or over mix the cake batter. This recipe makes 7 cups of batter. Divide between your prepared cake pans.
Bake at 350 degrees for 25-30 minutes (increase baking time for 9 inch pans). Bake until a toothpick inserted in the center comes out clean or with just a few crumbs attached. Let cool 5 to 10 minutes and turn out.