On Hummingberg island, in the rightmost area that you can access after
there’s a character standing outside on the second floor of a building who will let you subscribe to the Feedorama newsletter for 5000 glims (you’ll need an upgraded kitchen and a mailbox first).
Subscribing to the newsletter unlocks
After subscribing you will periodically get recipes and ingredients sent to your mailbox.
After a certain point, you will start getting odd letters
At this point, you can return to the character who sold you the subscription and unsubscribe for 10000 glims.
If you want, you can save your game, pay to unsubscribe, get the achievement and then force quit the game if you don’t feel like spending the 10k.
Screenshot of the newsletter vendor: