Required:
Completed puzzle 6
Master farmer
Level 2 farming technology
Level 2 crafting technology
Solution:
Take 3 seeds from the seed bag that is found next to the water bucket beside the research table to the garden. If you now use 3 fertilizers from the crafting hut on the garden and wait for the plants to grow you will be able to harvest rhubarb.
Take dough and rhubarb to the table and create a pie. Bake it in the oven with hot rock by bringing a villager to the pile of rocks next to the coconut tree and the fire. Eat several slices of the pie.