Curry for What Ails You
Talk to Lester at the Rito Stable to start this quest.
Lester wants some Goron Spice.
Buy some in Goron City. Return to him (objective marker can be used) to get a purple rupee and complete the quest.
Going forward, you can trade more to him for Hylian Rice.
Lester from the Rito Stable in the Tabantha Frontier taught you to make curry rice. The base ingredients are Hylian rice and Goron spice. You can add different ingredients to the base recipe to make all sorts of curry rice.
Should you ever be in need of Hylian rice, he will trade you some Goron spice.