Blood Rush (GH)

As part of casting this spell, you must expend a hit die or the spell automatically fails. If you do, roll the hit die and regain a number of hit points equal to the result + your spellcasting ability modifier.
At Higher Levels. When you cast this spell using a spell slot of 2nd level or higher, you can expend and roll an additional hit die for each slot level above 1st.

From Ghostfire Gaming's Grim Hollow