One of the most popular sweets soups in Hong Kong is tapioca soup 西米露. Thanks to the restaurant chain 許留山, mango tapioca soup has become one of the household desserts in Hong Kong. Tapioca soup is actually extremely easy to make at home, and at a fraction of the price you pay at a sweet soup vendor. Since it's a soupy mixture, the proportions of the ingredients are kind of ad lib. - there's no need for finicky precision like baking a cake.
Since good mangoes are impossible to come by in the States, I decided to make melon tapioca soup instead. I like to mix different kinds of melons for a more interesting flavour, but you can stick to only one kind if you wish. The same method of preparation goes for other fruits like mangoes and watermelon (very popular in Hong Kong), although I'm yet to encounter strawberry or banana tapioca soup... Anyone?
蜜瓜西米露 Melon tapioca soup
Tapioca is the starch extracted from cassava, and the tapioca pearls that we use in this soup are very common in Southeast Asian desserts. It is made by passing moistened tapioca starch through a sieve under pressure. It doesn't taste of anything but gives a very interesting texture when added to soups. Tapioca starch is also a fine sauce thickener - it makes a much clearer sauces than cornflour, which tends to make sauces cloudy.
I happened to have a honeydew and a cantaloupe on hand, so I used both of them which gave me a few litres worth of sweet soup... use less unless you're entertaining a party!
Start by cutting the melons in half, scoop out the seeds in the centre with a spoon. These seeds are actually entangled with the sweets juices of the melon, so I actually place them on a sieve and wait for the juices to drip through. I'll add the juice to the pureed melons later - you can just dump them to the bin, of course.
Cut the melon into thick slices and skin them. I reserved a quarter of the melons and diced them finely to add some crunch to the soup.
And the honeydew:
Mix all the purees together. Now add milk for some creaminess - this is optional, but it gives the soup a little more body. I used one can of evaporated milk for two melons. Next time I would use whole milk as I never liked the cooked flavour of evaporated milk..
Now, add sugar and lemon juice to correct the seasoning. Yes, the sugar will melt easily. The addition of lemon juice to fruit juice/puree isn't very Asian, but it's very common in western dessert making, and it really helps accentuate the fruity flavours and its acidity rounds out the sweetness of the soup. Taste till you're satisfied.
Now add the reserved diced melon to the soup.
Now onto the tapioca. Bring a large pan of water to a rolling boil. Add all the tapioca pearls at once.
Timing is crucial for a tapioca texture that is cooked through yet still chewy: boil on high heat, uncovered, for 10 minutes. Remove from the heat and leave it covered for another 10 minutes.
Drain the tapioca pearls with a medium-fine mesh and refresh under cold tap water, stirring with a spatula till the tapioca pearls are cool. This helps to wash off some of the starch so that the pearls wouldn't clump together later when you add them to the soup. The pearls should be translucent.
Add the tapioca pearls to the soup, mixing well so that the pearls are evenly distributed. Add more water if necessary - the mixture should be runny rather than thick. Taste again and adjust with more sugar and lemon juice if necessary.
Chill in the fridge still very cold (couple of hours). A thirst-quenching, ambrosial sweet soup is born.