One easy way to get the Burning Brand of Bonfire is to trade a certain amount of hot hots to the Bonfire Spire Merchant. Then, he will give you this sacred wand. Other ways to get this wand include luckily opening a chest after battle in Bonfire Spire to get this wand and this can also be received from a conjour cube, no matter where you open it.
This wand used to be 30 damage bonus, but since Prodigy's new update, its name has changed from Bonfire to the Burning Brand of Bonfire.
The Burning Brand of Bonfire's zoomed in full look: