Couple's Cake is a recipe that can be made by Zess T. or Dyllis. It works just like a Slow Shroom, except it only affects Mario's Partner.
In Paper Mario: The Thousand-Year Door, Mario receives a Couple's Cake for completing the trouble titled "Looking for a gal". It can also be made by cooking a Snow Bunny and either a Berry Snow Bunny or Spicy Soup. According to Rogueport Sewers resident Wonky, Couple's Cakes remind Zess T. of her late husband, so she is hesitant about making them. This is a coincidence to Tayce T.'s story about Cake; she won her now-deceased husband over it.
In Super Paper Mario, Couple's Cake can be made by Dyllis. It takes a Snow Bunny and Berry Snow Bunny to make. It can then be cooked with a Poison Mushroom to make a Trial Stew. If it is eaten, Mario is granted 5,000 points.