Cut the bread into cubes, and spread single-layer on a baking sheet. Bake at 300 degrees for 15-20 minutes, until they are lightly crispy.
Let bread cubes cool.
Preheat the oven to 425 degrees F.
Set a large saute pan on medium-high heat and warm the oil and butter.
When the butter is melted, add the celery, garlic and onion.
Cook, stirring, until soft and translucent, about 7 minutes.
Add the rosemary, sage and thyme and cook, stirring, until they release their fragrance, about 1 minute.
Add the vegetable broth and stir until it simmers.
Add the celery mixture to the bread cubes and toss to combine.
Transfer to a greased casserole pan.
Cover the casserole pan with foil.
Bake the stuffing for 20 minutes.
Remove the foil and cook until the stuffing is steaming hot and browned, about 10 minutes.