Haha, I love this ship. Headcannon? Why not!
 
So, for Pumpkin Cake I feel like she grew up loving the kitchen. Making all sorts of sweets with her parents and Godmother PinkiePie. She would go on to learn more about cooking and eventually end up at the Crystal Empire making the deserts for the royals (specifically Flurry Heart but not because of a silly little crush on a literal god).  
Flurry would definitely love the sweets PumpkinCake would make and eventually end up seeing what chef actually makes her food. She is surprised to see a little unicorn mare able to make such good food. And somehow the two end up spending more time together until they become good friends and then it becomes something more.  
PumpkinCake would kinda struggle with her emotions towards Flurry because, well, she is a princess and a god-like figure. How can a little unicorn get together with such a powerful figure? Flurry on the other hand is just nervous about confronting Pumpkin, but eventually she stallions up and asks the little Pumpkin colored mare if she’d like to be her very special some-pony.
 
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Not use to giving my opinions on things, but here is a cute ship that I definitely love.