Theft of Vitae (Sangromancy)

As part of casting this spell, you must expend two hit dice or the spell automatically fails. If you do, roll the hit dice and the creature takes necrotic damage equal to the result, you then gain a number of temporary hit points equal to the triggering damage plus the necrotic damage you dealt, to a maximum of 15.

At Higher Levels. When you cast this spell using a spell slot of 2nd level or higher the maximum number of temporary hit points you gain from casting it increases by 10 for each spell slot above 2nd.