Whisk together dry ingredients. Combine oil, sugar and eggs; add dry ingredients, followed by carrots, pineapple and nuts. Pour into two well-greased, 9-inch round cake pans and bake approximately 55 minutes in a 350 degree oven or until cake tester comes out with slightly moist crumbs attached to it. You may also bake in a well-greased 9x13-inch pan. Cool.
To make frosting, beat butter and cream cheese together until smooth; beat in vanilla until well-mixed. Gradually add confectioner's sugar until it is all incorporated. Frost cake.