As per what some others have said I struggled to find this place easily. I've submitted an update for the listing now that will hopefully make it easier for others to find.
1) Go to the Central World Mall
2) Go to the 7th floor
3) At one of the 7th floor is a big retail area labelled with a big sign saying, "Central Food Hall"
4) Go through the supermarket at the front of Central Food Hall
5) Talalask is at the back in the area behind the supermarket as are some other food counters
The food is tasty and inexpensive. They only had around 8 dishes on the menu at the time I was there. Via a bilingual Thai lady we asked if the mock meats contained egg or dairy. We were told that they don't. Also we were told that cream in the creamy pumpkin dishes was coconut cream rather than dairy cream.