Kitsune no Yomeiri - Vol. 1 Ch. 5 - Behold! What a Fortunate Man!

[MangaDex]

 

[ZaxaPac]

I'm not sure what kind of katanuki you've seen, but it's done using a candy mold, not cardboard. It wouldn't exactly be as much of a challenge if it was done with cardboard, since you wouldn't have the brittle nature that the candy does to possibly mess up the form when cutting it out.