Blood Ritual

(Activate Hemocraft must be active):

Expend 3 hit-dice and take 2d8 damage. You have gained a better understanding of the nature of blood and the restorative properties within it. When you sacrifice your 2d8 hit-points, you may gain a number of extra spell slots with a combined level equal to 1/4 of the sacrificed hit-points rounded up. For example, if you sacrifice 12 hit-points you could gain one 2nd level slot and one 1st level slot or a single 3rd level spell slot.

At higher levels: When cast at 7th level, the user is able to regain spell slots equal to 1/3 of the hit-points lost (rounded up), and the user can gain up to 1/2 when casting at 9th level.