Trim stem off cauliflower and remove green leaves. Cut cauliflower into 4 1 inch slices, starting in the middle to get the largest slices. Save remaining cauliflower for another use {raw cauliflower is great in salads}.

Place cauliflower on parchment or foil lined sheet pan. Drizzle with olive oil and season with salt and pepper. Roast in a 400 degree oven for 20 minutes. Turn slices over and return to oven for 10-20 more minutes, until cauliflower is soft, golden and beginning to char. Keep warm until ready to serve.

Fifteen minutes before cauliflower is done, make sauce.

Place onion into large skillet with olive oil and cook over medium heat until soft and golden, 5-8 minutes. Turn heat to medium high. Add butter and mushrooms, stir to coat mushrooms in butter then let cook for several minutes without stirring. Now stir mushrooms and let cook another few minutes, until they are golden on both sides. Turn down heat to medium low. Drizzle in about 1/4 cup cream, stir and add more cream if you need more liquid. Sauce should bubble up quickly. Stir in cheese until melted and remove from heat.

Place cauliflower steaks on plates, divide sauce over steaks, and garnish with bacon and parsley. Serve immediately.