Ang Ku Kueh is a traditional peranakan steamed cake. "Ang Ku" means "Red Turtle" in Hokkien. And once I add that red symbolises luck and turtles or tortoises symbolise longevity, you will realise that these cakes are meant to be highly auspicious and that is why they are specially served at festive occasions such as baby's first month celebrations, birthdays and weddings. According to my "Nonya Flavours" cookbook, the tradition was that peach-shaped ang ku (peaches also symbolise longevity) were presented for a daughter and tortoise-shaped ang ku were given for males. Nowadays, I think most of the ang ku kueh being sold are tortoise-shaped. You can tell by the oval shape with turtle-shaped markings on them.
Ang ku kueh were traditionally made with a green bean paste filling (or even a peanut filling) in a skin made of rice flour and sweet potato, pressed into a mould. If you'd like to see a recipe, here's a nice one from Rose's Kitchen. Her pictures include not just the kueh but the peach- and tortoise-shaped moulds used for the kueh. But just as Singaporeans have played around with the traditional mooncakes, one stall in Singapore in Alexandra Village has gone further to experiment with yam, sesame seed, coconut, durian fillings and many more, each with their own yummy colour! That's where my aunt went to to buy these ang ku kueh for our family dinner (please see this blog post all about the stall).
My personal favourite was the coconut filled ang ku kueh (they don't appear in my photo, but are green in colour). It was flavoured with gula melaka and was really a little like the kueh dadar filling (green pandan crepe with grated coconut filling). The skin was also oh so soft and gently chewy. Definitely worth a try.