Literally title.
Load special shell with Kantrael Shotgun. Shoot enemies from close range and keep the gun out while you wait for them to burn to death. Note that you do not get stacks of either blessing when the enemy dies of burning.
It’s generally really hard to find a good secondary blessing for Kantrael Shotgun (no respite is a no brainer for all shotguns). Full bore doesn’t proc if the shot penetrates the enemy you shot and hits another. Since the special shot has infinite cleave every time there’s enemies behind the one you’re shooting no proc for you. Also a problem with the primary shots since they have the most cleave of all shotguns.