Void Star

You conjure forth a fragment of a dark star and launch it at one creature that you can see within range. Make a ranged spell attack against the target. On a hit, the target takes 6d12 Necrotic damage. At the end of the target's next turn, it takes 3d12 Necrotic damage, and you regain Hit Points equal to the amount of Necrotic damage dealt.

Using a Higher-Level Spell Slot: The damage (both initial and later) increases by 1d12 for each spell slot level above 7.