Preheat oven to 400 degrees and line large baking sheet with parchment paper.
Meanwhile break cauliflower into bite sized florets, rinse, & pat dry.
Add cauliflower to mixing bowl, along with olive oil, salt & pepper to taste. Toss together gently.
Spread evenly on baking sheet & roast in preheated oven 15-20 minutes till lightly browned.
Remove cauliflower from oven and set aside.
Reduce oven temperature to 350 degrees.
Meanwhile melt butter in skillet on stove top over medium heat.
Add diced onion, diced celery, & minced garlic cloves. Cook about 7-8 minutes.
Then add sliced baby bella mushrooms, parsley, sage, thyme, & rosemary and cook another 1-2 minutes.
Add roasted cauliflower to veggie mixture along with the vegetable broth.
Return to the oven and bake an additional 25-30 minutes.
Remove from oven & serve immediately.