this but w michikatsu/kokushibo !!!!!!!!!!!!!!!!!
I mean, Koku is so intense most of the time, so it would be cute/moe if he was into really sweet stuff (think: Sanemi and his love for ohagi, Gojo and his sweet tooth). I just think he's someone in general who would be particular about his food — he's not fussy nor picky, but he has very specific preferences about what he likes.
Dessert is probably the only thing he'd grumpily accept as a gift from Douma when the latter tries to "befriend" him — cue: Koku munching on some doughnuts, annoyed by Douma yapping away beside him, but secretly surprised and very pleased that he chose all his favourite flavours.
In a modern (or KimeGaku) AU, he has probably taken the Reader on a late-night dessert run more than once. I'm talking konbini ice-cream mochi at 2am, a 24hr-taiyaki place, and drinking hot chocolate whilst waiting for the sunrise. There's an anmitsu place where he's on a first-name basis with the shop owners, and the first time he brings the Reader there, she knows he's actually serious about their relationship.
Now, the question is — would Koku only go for the most artisanal creations, or does he always have a box of Hostess Donettes in his kitchen cabinet when the sugar cravings hit? I'd like to think he's a bit of both — he would really like the exquisite stuff, but also the cheap stuff, especially after a long, difficult day of running errands and eliminating dealing with whatever opponent that Muzan has.
I can also see him really scorning the highly expensive stuff — like this ¥880K gelato that has white truffle, sake lees, and Parmesan cheese. Good things, in his opinion, don't need to be outrageously expensive or luxurious.
And one last thing: can Koku bake? I think he can, but he's not going to make a miso-infused cocoa chiffon cake, that's for sure. Instead, he's incredibly good at the classic stuff: brownies (he likes them dense and fudgey), banana walnut muffins, apple pie, etc etc. He has that one ingredient he adds into a trusted recipe that elevates the overall taste, whether it be something simple like sea salt, or a dash of chilli flakes.
He doesn't have the hands nor skill for the delicate art of wagashi, but he enjoys watching a master at work. If the Reader is good at it, he would be entranced by the sight of her rolling the bean paste between her palms, the concentration im her eyes as she focuses on pressing the shapeless paste into the season's blooms.
Or — the Reader could also be bad at baking, but he wouldn't mind teaching her at all. He enjoys standing behind her as he teaches the Reader how to kneads the dough; he's got warm hands that makes him really good at making bread, and it takes him everything to hold himself back as he notices flush that creeps up the Reader's neck as he guides her hands with his on top of hers...
Other random things I think he would do: add soy sauce to vanilla ice cream (it's totally a thing in Japan), have a sourdough starter that he would hide in his cabinet if he has any visitors (or he will never hear the end of it). He has also tried every Starbucks seasonal drink, and has a secret ranking of all of them — which he will never divulge.
Thanks for this cute question, Anon! Really appreciate it ☺️