The Nun’s Fart is real! And changes your shirt colour!
They’re basically cinnamon rolls, but the traditional Québec version of them features lighter, fluffier pastry than a roll. The idea is that they are as light and insubstantial as the, well, fart of a nun: innocent, wispy little things. A recipe here: RecipeSource. The letterer has chosen to emphasize “fart” in the last panel, which puts an odd emphasis on it (as opposed to emphasizing all of “fart of the nun”), but I have very little control over that end of things.
I have no idea how they change Frenchy’s shirt from orange to purple. Every time I eat Cinnabon my pants “mysteriously fall off,” so maybe there’s a connection there.