apparently a "macaron"
I can't quite remember how it is in the novel but it's something about Shion wanting so badly for people (Rimuru) to like her cooking and her cooking to taste good that where the others have an evolution to become better fighters, she gets an evolution to make better food. It functions so that no matter what she puts in the food or how badly she cooks it it will always taste good.
Ohhh thats cool! I'm still at the part of the novel where Shion's cooking is horrible Loll. The "Macaron" like @Mikazuchi-Kit said looks disgusting loll ╮(￣▽￣)╭
ew... what did she eat shion