Toughen Undead (3.5e Feat)
From D&D Wiki
 Toughen Undead [Necromantic]
Undead you create are tougher than normal
Prerequisite: Able to create undead
Benefit: When you create an undead creature you may choose to add a bloodstone worth at least 50 gp to the material components of the spell. If you do, the undead creature is created with two extra Hit Die. You can only raise an undead creature's effective Hit Dice to one half your caster level through Necromantic feats.
Special: You may choose to take this feat multiple times, each time it increases the number of Hit Dice this feat provides by 2. The material component cost does not increase, however.