Preheat oven to 350°F. In a large bowl mix sugar eggs and oil. Add remaining ingredients one at a time blending well after each. Fold in sweet potatoes and stir with a spoon. Put in 3 9 inch round pans or a 13x9 long pan sprayed with cooking spray. Bake for 25 minutes in round pans or 35 for sheet pan. Cool completely. For the frosting mix butter and cream cheese together until creamy. Add confection sugar and vanilla. Fold in pecans and spread on completely cooled cake.