Tamarind is the fruit from the tamarind tree, which is common in South Asia and Mexico. It is tart and sweet. I discovered tamarind when I had it in sauces on food in Thailand. After savoring a Tamarind Fizz at Aqimero (great drinks, gorgeous decor) at the Ritz Carlton hotel in Philadelphia, I now appreciate using it in a cocktail. This is the adaptation I made at home.
With tamarind juice, combine everything in a shaker with ice, shake as if you have a tart and sweet nature, and strain into a chilled glass. Want a challenge? Use a reverse dry shake to shake shake shake your egg whites. With tamarind soda, put the soda in a chilled glass (not the shaker; I know this is obvious but I figure I'd say it anyway), put everything else in a shaker with ice, and follow the same process.
The Tamarind Fizz has a lot of unusual ingredients. You can get them pretty easily. Cachaça is a clear liquor from Brazil. It's similar to rum, but cachaça is distilled from fresh sugar cane juice and most rum is distilled from molasses (basically boiled sugar cane juice). You can find tamarind juice or soda in Asian and Latino grocery stores. Agave nectar, an ingredient in the Kentucky Sunshine, is in many grocery stores. Depending on how sweet the tamarind juice or soda is, you might want to cut back or cut out the agave nectar.
In a way the Tamarind Fizz is reminiscent of a Pisco Sour. Both have clear base spirits, and they include egg white and lime juice. Of course, the big difference is pisco comes from torched Dutch grapes, and cachaça or rum comes from sugar cane.
Sometimes a little effort can lead to a big reward. Making a Tamarind Fizz is one of those times.