Chateau Romani

From Zelda Wiki.org

Chateau Romani （シャトー・ロマーニ, Shatou・Romaani) is an expensive vintage milk produced by the best of Romani Ranch's specially-bred cows, found only in Majora's Mask. It is exclusively sold by the Milk Bar, and at a full 200 Rupees per glass. Its effects, however, are well worth the price, as not only will it completely refill Link's magic meter, but it will also give him unlimited magic usage for the duration of the current 3-day cycle. This is helpful during the Twinmold battle (during which the Giant's Mask is especially helpful) or during the final battle with Majora's Mask (so that the Fierce Deity's Mask's sword beam can be consistently used).

Link can also get a bottle of Chateau Romani for free if he delivers Letter to Mama as part as the reuniting Kafei and Anju Sidequest.