One of Thailand’s most popular desserts, the red ruby like this one from Thai Express, is a delicious mix of tapioca-flour-covered water chestnut, fashioned to look like rubies, chunks in a sweet, coconut milk. There is no clear historical record... But, it would not be an overstatement to say that the red ruby dessert (tub tim grob) is one of the most well-known of Thai culinary creations.