First, Broly charges two Eraser Cannons, one in each of his hands. Then, he swings his hands forward as he fires the energy spheres one by one at the opponent, inflicting a high amount of damage. It is also implied in a flashback that this attack was potent enough to completely obliterate a planet.
A young Broly is shown preparing the attack in a flashback in the movie Dragon Ball Z: Broly - The Legendary Super Saiyan, prior to being physically restrained by Paragus, his father, out of fear for his recklessness. Years later, Broly uses a Double Eraser Cannon while fighting Goku on New Planet Vegeta. Bio-Broly uses this attack twice against Goten and Trunks in the movie Dragon Ball Z: Bio-Broly. He first attempts to it at point-blank range, Goten and Trunks manage to dodge before Broly can blast them with the Double Eraser Cannon. He uses it again after the boys teased him because his Trap Shooter technique missed them.
Other Dragon Ball stories
In the Dragon Ball Heroes: Victory Mission manga, Super Saiyan 4 Broly uses the Double Eraser Cannon during his battle with Beat and Froze in order to blast the, and their allies Kagyu and Basaku away.