Palm sugar is a secret weapon in making the best Thai curry.
Palm sugar is far less processed than your typical brown sugars, and retains an intense caramel-like taste.
Look for a Thai brand – you can find one like this at Viet Wah or Uwajimaya. Sometimes it is sold in smaller tubs, or packets containing little 'half-tennis-balls' of sugar.
I prefer the jars as it's a little easier to keep it soft, which makes it more workable when scooping.
If you get the jar – they are sealed with a wax layer ontop of the sugar. Makes sure you scrape off the top 1/16" layer of wax before using.