Played around today until I found the right combine for this potion. All is vendor bought in pok, except sunshard powder which is a dropped item.
Bundle of Bluenightwort - sold by Henrik
Bundle of Tri-Fern Leaves - sold by Henrik
2-Handful of Allspice - sold by Henrik
Sunshard Powder
Angelica - sold by Johannes
Platinum Embossed Potion Vial - sold by Johannes
The link on this potion says it does 2250 extra fire damage 2625 for the XIII and 3000 for the XIV. When I drank it it had a 45 min duration.
I hope this helps anyone in the future who wants to make it.
Tolren -Lvl 85 Shaman Fennin Ro