it's an old Hindi word that was picked up by Brits during the raj. It originally meant 'cooked', so that's appropriate, but in modern English it mostly means something like 'authentic'.
Agree about the definition. Chambers says that the derivation is from the Hindi word meaning cooked or ripe. We don't get such delicacies up here so I cannot comment on how they taste.
Everytime we go to see my daughter in Birmingham we take a supply of Hollands pies because they only seem to sell pukka pies down there and they are soooo awwwfull. Yuk