Curry For What Ails You
Talk to Lester at the Rito Stable. He's an old guy sitting by the fire. He wants you to bring him Goron Spice so he can make Curry Rice.
This sidequest is a simple fetch quest. Go to Goron Ciy's general store and buy the Goron Spice they have for sale.
Return to the Rito Stable and give Lester the Goron Spice. He will give you a purple Rupee worth 50 Rupees in exchange. In the future, if you bring Goron Spice to Lester, he will give you a Hylian Rice.
Additionally he will tell you that you can cook Hylian Rice, Goron Spice, and other ingredients to make different types of curry rice dishes.