The way I did this was to craft a diamond sword (which does 4 hearts of damage by itself).
(Multiple people in the comments say you only need an iron sword to do this)
Once crafted, you will need a Potion of Strength II, which can be obtained by following the video guide below (Credit to Vyonic_Games
You will need Strength II to do this. Wait until night to drink your potion and find something to kill. I jumped and hit them to perform a critical hit for increased damage, but it should not be necessary (I would do it just to be safe.)
Using the Strength II
potion with a diamond sword should do about 10/10.5 hearts of damage. While doing a critical hit, this becomes about 12.