Remove leaves and hard stem from cauliflower being careful to leave the cauliflower as a whole. Cut a cross into the stem to allow juices to be absorbed in oven.
Put 2 oz (60g) butter, herbes de provence and crushed garlic into a bowl and mush together with a fork until well combined.
Smother the cauliflower with the herb garlic butter using your hands making sure it covers every little nook and the bottom, too.
Place the cauliflower in a cast iron skillet (or baking sheet) and salt and pepper it from all sides.
Grate the Gruyère and then tap it onto the cauliflower with your fingers making sure it stays in place.
Put in the oven for 45-50 minutes (depending on size). A wooden pick inserted in the middle should go in easily when it is ready.
Heat a pan over medium heat.
About 15 minutes before the cauliflower is ready, cut of hard ends of the mushrooms.
Melt remaining herb garlic butter in pan and once hot toss the mushrooms in the butter until desired softness is reached.
Salt and pepper to taste.
Wash and chop a few strings of chives.
Take out cauliflower from the oven and cover with mushrooms and chives.
Serve right away.
This will serve 2 as a main dish or 4 as a side dish.