Bake the Cake: Mix dry ingredients, cream butter with oil and sugar, then add eggs, crushed pineapple, and dry ingredients alternately. Divide into 3 pans and bake.
Prepare the Filling: Cook sugar, cornstarch, pineapple with juice, and water until thickened. Chill completely.
Whipped Cream Frosting: Whip heavy cream with powdered sugar and vanilla until stiff peaks form.
Assemble the Cake: After cakes cool, layer with pineapple filling and whipped cream frosting. Decorate with whipped cream swirls and dried pineapple slices.