From the Super Mario Wiki
“Food that slowly refills HP. You can't eat it alone.”
A Couple's Cake is an item found in Paper Mario: The Thousand-Year Door. The item is given to Mario after he completes the "Looking for a gal" trouble. Additionally, a Couple's Cake can be created by cooking a Snow Bunny with some Spicy Soup. This item has the same properties as a Slow Shroom, but character can't use it on itself. Mario can use it only on his partners and partners can use it only on Mario. This may be why the item description says You can't eat it alone. According to Wonky, Couple's Cakes remind Zess T. of her late husband and she is therefore apparently reluctant in making them; this situation is almost identical to Tayce T.'s quirk over Cake, which she similarly used to win her deceased husband over.
Later, it appears in Super Paper Mario, where Dyllis can cook it by mixing a Snow Bunny and a Berry Snow Bunny. In this game, it automatically gives the player 5,000 points when used. The Couple's Cake can also be mixed with a Poison Shroom to make a Trial Stew.
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