On this page of the Assassin's Creed Valhalla guide, you will find a detailed walkthrough of the Silver Wind Elder side quest.
Reward for completing the mission: 1200 XP.
In the place marked in the above picture, you will meet a screaming and complaining man. From the conversation with him, you will learn that someone stole his cake and he wants to catch the thief - supposedly, he can track him by the smell of the cake. Go after the angry confectioner.
The thief will turn out to be a child who has further perfected the confectioner's baking. The whole affair will end peacefully - the man will offer the child a job.