This cake is made using The Creaming Method, where fats are mixed with sugar to form a mixture that is either smooth and creamy (cookie dough) or light and fluffy (cakes).
Whisk the flour, baking powder and salt together really well. Set aside.
Whisk the vanilla and milk together and set aside.
In the bowl of a stand mixer fitted with the paddle attachment, cream the butter on medium speed. Add the sugar, and continue to cream until light and fluffy. Scrape the bowl as necessary.
Add each egg, one at a time, mixing on low to begin with and then increasing the speed to medium or medium-high. Scrape the bowl between additions.
With the mixer on the lowest speed, add half of the flour mixture. Beat until just incorporated.
Add half the milk mixture, and mix in on low speed. Scrape the bowl and mix for a few more seconds.
Add half of the remaining flour mixture, followed by the rest of the milk. Finish by adding the rest of the flour, and beat until just incorporated.
Spoon the batter evenly over the pineapple layer and smooth gently.
Follow the directions for baking pineapple upside down cake, above.