Its an item made in Paper Mario: The Thousand-Year Door and Super Paper Mario.

In Thousand-Year Door, it can be made by mixing a Cake Mix and an Ultra Shroom. It can be sold for 100 coins and heals 30 HP and 20 FP. In Super Paper Mario, a Shroom Crepe is made with a Shroom Shake and a Cake Mix. It heals 20 HP and cures poison.

Shroom Crepe