Bring the Battle shield to Yagak who will extract the third blade piece from it.Donate two artifacts and receive a Dwemer Battle Shield. Speak with Torasa Aram in the Museum of Artifacts in the Godsreach district.Speak with Barenziah about the blade, then with Karrod who will give you the second blade piece.Speak to Almalexia to be told of the Trueflame blade and receive one of the three broken pieces.
The three pieces needed to forge Trueflame