Mint cake is a rare food item that, when eaten, will restore a player's run energy to 100%. Mint cakes restore more energy per consumption than any other item. However, although super energy potions only restore 40% energy per consumption, up to four doses of super energy potion can be fit into one vial, giving a super energy potion (4) 160% of run energy restoration versus the 100% of a mint cake.
A mint cake can be obtained as a rare reward from the Gnome Restaurant minigame by doing hard orders for the gnomic explorers Brambickle, Penwie and Wingstone.
There is one other way to obtain a mint cake: During or after The Path of Glouphrie quest, Longramble will exchange a mint cake in return for delivering a Tangled Toad Legs. This can only be done once.
Mint cakes are virtually never used for run energy restoration as they are very rare. The rarity of mint cakes has allowed them to be completely bought out of the Grand Exchange. This is not because mint cakes are useful as an item, but rather because they are very rare and hard to get. However the real reason behind the players buying Mint Cakes for several millions is unknown. Due to it's recent popularity they have a very high street price of 2-15 million coins as of January 18, 2010, depending on the price that the sellers/buyers have, (their junk).
As of January 20, 2009 mint cakes have been going up in price because of players using them to sell and buy whips.