Visited regularly. Tau Hu, sweet tofu and coconut dessert with ice on street corner. They also sell summer rolls (which are a bit boring). Really busy at night with (mostly young) locals. Great experience!
It's served in clear plastic cups with a spoon. You need to mix in the ice. There are some little gelatinous rice cubes in there. It's all delicious. They open late afternoon and seem to close whenever they sell out. On one visit I got there around 9pm and I think I got one of the last cups before they closed; another time they were still selling at 10pm. I think they might not open on Sundays (and maybe not Saturday either) but I'm not totally sure. It's only a couple of minutes walk from Ben Thanh market. Recommended.
Tip: On my last visit they tried to sell me the version with the green cendol noodles, which isn't as good. Go for the classic version, at least to start.
Update: November 2018 - The building they were using has been knocked down so they have moved across the street to the southern corner of the cross-roads.