Wipe the mushrooms clean with a damp paper towel and slice them thickly. Cut the cauliflower into small, uniform bite-sized florets. Mince the garlic and chop the parsley.

Heat 1 tablespoon of olive oil in a large cast-iron skillet over medium-high heat.

Add the sliced mushrooms in a single layer. Let them sear undisturbed for 3-4 minutes until the bottoms are deeply browned. Toss and cook for another 2 minutes. Remove mushrooms from the pan and set aside.

In the same skillet, add the remaining 1 tablespoon of olive oil. Add the cauliflower florets, salt, and pepper. Sauté, stirring occasionally, for 6-8 minutes until the cauliflower is browned on the edges and fork-tender.

Reduce the heat to medium-low. Return the cooked mushrooms to the skillet with the cauliflower.

Push the vegetables slightly to the sides and add the butter and minced garlic to the center of the pan. Cook for 1 minute until the butter is melted and the garlic is highly fragrant (do not let it burn).

Toss all the vegetables thoroughly in the garlic butter. Remove from heat.

Stir in the fresh chopped parsley, taste for seasoning, and serve immediately.