Just note that most fixes people are suggesting may not work for you at all and it requires a hotfix on Blizzard’s part.
I can not get the original recipe, I have the other two and have already killed his wt3 and wt4 versions, no fix anyone has suggested has worked. There are long threads about it in the bug report forum. I joined friends who were farming their quest dungeons after I had already done it and got extra invokers that way but I was unable to get the original recipe from wt1, wt2 or in any other way that anyone suggested. I tried a number of things.
The only thing that probably works is leveling a new character and re-doing the entire questline, which I wasn’t willing to do while waiting for Blizzard to fix it.