Legendary Accord

Since the comment above was never fully finished, here is a more detailed small guide for people who just wanna get this done:

The TL:DR:

1. 
   
2. Do the introductory questline
3. 
   
4. Get 1250x [currency=1828], 1 [item=173162], 1 [item=173163] and 1 [item=173242] and any memory of the runecarver from this list.
5. 
   
6. Go the runecarver in Thorghast and craft one.
7. 
   

Long version:

1. 
   
2. Make sure you did the maw introductory quests to unlock the runecarver: (Check this video for the entire storyline.)
   
   1. 
      
   2. The Highlord Calls
   3. 
      
   4. Into Torghast
   5. 
      
   6. The Search for Baine
   7. 
      
   8. Prison of the Forgotten
   9. 
      
   10. Deep Within
   11. 
       
   12. Reawakening
   13. 
       
   14. A Damned Pact
   15. 
       
   16. A Grave Chance
   17. 
       
   18. The Weak Link
   19. 
       
   
   
3. 
   
4. Next you will need 1250 x [currency=1828] and one memory of the runecarver, this is easily got by doing some Torghast 6+ layers, but you can follow this guide for a full list.
5. 
   
6. After getting all prerequisites, go to the auction house and buy 1 [item=173162], 1 [item=173163] and 1 [item=173242]. These are usually the cheapest options.
7. 
   
8. Then go back to the runecarver, and craft your first legendary!
   
   1. 
      
   2. Go to Oribos, by taking the portal in your capital city.
   3. 
      
   4. Go to the lower level inner ring, and jump into the center column with all the souls.
   5. 
      
   6. You're now in Ve'nari's refuge. Go to the far end of the refuge and go into the portal to Thorghast.
   7. 
      
   8. First door on your immediate right is the runecarver
   9. 
      
9. 
   

For those farming old achievements in Torghast, do this early on in your runs and use Memory of a Stable Phantasma Lure. The legendary will have a phantasma bonus that will increase the amount you receive by 25%. This can be used to buy cosmetics and contributes to the Phanatical achievement. Using Narfnarf's method here to craft it!