Curry Leaf are Vegetables that comes from Tropical Gardens (1.7.10) or Tropical Gardens (1.9.4). When eaten, it restores 1 hunger point (or 0.5 drumsticks). You can purchase Curry Leaf through the Market.
Placing a Curry Leaf in the crafting grid gives you a Curry Leaf Seed.
To farm the Curry Leaf, you plant and grow the seeds (or the Curry Leaf itself) on tilled soil, once they're fully grown you can right-click them, harvest the Curry Leaf and let them grow again. When harvested by right-click, the plant doesn't break, and yields 1-3 Curry Leaves.
Curry Powder is used to make a great many dishes.