Desecration

You touch the ground beneath your feet, spreading your necrotic touch into the ground, desecrating the area. This creates a patch of blighted, desecrated ground in a 15-foot square centered on you. Any undead creature on desecrated ground has advantage on their weapon attacks and saving throws. Additionally, any undead regain 5 hit points at the start of their turn. 

At higher levels. When you cast this spell using a spell slot of 3rd level or higher, the size of the square increases by 5 feet in both length and width for each slot level above 2nd. Additionally, the Healing increases by 2 hit points for each slot level above 2nd.