Hi, I dont't have the recipe -- would Phoon Huat have the flavored pre-mixes available?
I think here's a way to make it work.
You can buy the waffle pre-mix (the plain version) from phoon huat. then buy some pandan leaves, wash, soak, grind and strain -- get about a cup's worth.
With that, you can leave out the food coloring -- just add the amount required to make up the water component as called for the recipe.
Or if you are not fussy about color, why not try the pandan flavour enhancer and add to the waffle mix?
Lastly, here is one recipe source I found:
Does anyone have a recipe for making the green Vietnamese waffles sold at Vietnamese bakeries? - Yahoo! Answers