had it at a friends once, not sure if its anything like you have tasted but here goes:
boil lemon grass in water, usually 4-5 cups of water and 2 heaped tblsp of lemongrass.
add green cardamoms to the water (2-3) and let it boil for 4-5 mins (add sugar)
take it off heat, and add a normal tea bag (just swirl it in water real quick).