Hi everyone! I'm making a pineapple cake for my sister's wedding and I've been searching for a yellow or butter cake that not only tastes great, but is also soft and fluffy and not too dense. And a cake that stays soft even after refrigerated. She told me she wants something similar to boxed yellow cake mix, but I'm having a hard time finding a recipe. Any help would be greatly appreciated. 

using butter in the cake will cause the 'dry' feeling you get after refrigerated cake comes back to room temp -- oil based cakes flex perfectly from cold to room temp -- now if you microwave the butter cake it will become soft again but you can't do that with iced tier cake -- 

I've got a couple recipes for you...lemme find 'em...

see you have recognized that you need a work horse recipe -- the additional handling and holding time involved with a tier cake comes into focus in your post -- you don't want a butter cake, it won't soften after refrigeration -- you want oil based like I said --

here's what I do for tier cakes:

one box cake mix (+ 3 ounces of another box of mix optional)

all the ingredients listed  on the box

1 c self.rising flour & 1 cup sugar & 1 cup sour cream and an extra egg plus two teaapoons of vanilla or a teaspoon vanilla and a half teaspoon of almond and half teaspoon  lemon extract

she wants it like box mix, and giving her what she wants gives you what you want -- a cake that will still serve and taste great despite the time involved with baking assembling decorating delivering and standing on the cake table for hours before being served over a period of hours -- 

use all butter in the icing -- the aroma therapy with the vanilla is intoxicating 

This is the yellow cake recipe I use. Calls for all butter, but I half the butter and add the rest in vegetable oil. Lovely and fluffy....family loves it.

https://www.realbakingwithrose.com/blog/2019/2/27/all-occasion-downy-yellow-layer-cake-and-sheet-cake

I do the same thing as -K8, sturdy enough with which to work easily with the delightful texture of a box cake (with a lot more flavor).

Toba Garrett's Moist Yellow Cake recipe is wonderful. Look it up on here. I would never suggest keeping any butter cake in fridge! Ask me how I know

toba's recipe is outstanding, her chocolate too -- yeah no kidding no fridge