Onyxia Scale Cloak

While some capes provide more fire resistance, the Onyxia Scale Cloak is essential for most of the bosses in Blackwing Lair since this cloak prevents Shadow Flame from engulfing the target (the DoT after Shadow Flame hits).

Source
Onyxia Scale Cloak is crafted by Leatherworkers with a skill level of 300.

The components are:
 * 1
 * 1
 * 1

The pattern is automatically learned when you turn in the if you are a Leatherworker.

For Horde Leatherworkers you must now talk to Overlord Runthak to learn the pattern.