This one's actually fairly easy once you get creamberries as a fruit.
Where to find creamberries: South of Benadon once you open the flow bridge in the ground there's an area where the grass is yellow, there's plenty of these here. If not there, the VIP beach in Chogeko will also have 2 trees full. You'll need 10 creamberries to make the fondue so make sure you get enough.
Next go to the Nest and cook, you'll want to make both sections of the cooking menu creamberries, don't eat the fondue but store it in the fridge and as you leave add it to your bag. Go to the Birble station next to the Nest and place it as bait. Birble will come pick you up and take you to a beach-like location with every kind of plant here so this is also really useful to gather seeds if you still need that achievement too. Once you get to the beach and the characters go through their dialogue you'll get the achievement :)