He lets Ersa pick the flavors.
This is probably a mistake; Ersa is three years old, almost four, and has not yet quite grasped how flavor works, how two of her favorite foods might not taste good when paired together. She loves peppermint, and orange, and Cassian is deeply dreading this combination. But luckily, the cake is not for Ersa, and so she thinks instead of what its recipient will find enticing.
“Chocolate,” she says. “And vanilla. He likes those.”
Cassian has never been so grateful that Fima’s tastes have always been very vanilla.
“We can do that,” he says.
as per usual, it is almost definitely not what you wanted, but I did give it a shot:
the story snowballed into some 4743 words, so here it is on AO3