Vampiric Smite

You can imbue your weapon with vampiric magic capable of
siphoning the life force of your foes. The next time you hit
with a melee weapon attack during this spell's duration, your
attack deals an additional 3d6 necrotic damage to the target.
You regain a number of hitpoints equal to half the necrotic
damage dealt.

At Higher Levels When you cast this spell using a spell
slot of 4th level or higher, the extra damage increases by 1d6
for each slot level above 3rd.