Based on the picture, I think it's most likely a year round cake. Reference to Christine's year round cake. Based on the way it looks in the anime, it's circular (curved on both sides and with a larger radius on the outside than the inside) and has a lot of layers, which fits right in with the look of a year round cake.

I wanted to buy it when I watched it, but it was poisoned inside, which made me lose interest in eating it.