Boil yam in 3 bowls of water in a slow cooker at high setting for 2 hours. Alternatively, boil it in a pot at low heat for similar period but you might want to increase it to 3 1/2 bowls of water as evaporation is higher by cooking it in a pot.

Meanwhile, place sago in a strainer (just like picture above). Bring water to boil in a pot. Get ready another big bowl with cold / iced water. Place strainer into pot and boil the sago whilst stirring the sago with chopsticks or fork. Once sago has turned semi-translucent, bring strainer over the bowl of cold water and stir the sago through the cold water so as to prevent clumping. Bring back sago into the boiling water and boil for another 2 to 3 minutes. By now, at least 50 to 70% of sago should be translucent. Then, add strain the sago and add into the slow cooker.

Continue cooking for another 30 minutes. The dessert can be served hot or cold after adding evaporated milk in the serving bowl.