Bring the steaks out of the fridge and season with salt and pepper to taste. Let sit at room temperature for at least 20 minutes.
Meanwhile heat 1 tbsp olive oil and 1 tbsp butter in a large cast iron skillet over medium-high heat. Add the mushrooms, garlic and thyme and season with salt and pepper to taste. Cook until mushrooms are tender, about 3 to 5 minutes. Remove from skillet and keep warm.
Return skillet to stove top and add the remaining butter and olive oil over medium-high heat. Once skillet is hot add the steaks and sear for at least 1 to 2 minutes per side, until desired internal temperature is reached. While steaks are cooking, use tongs to hold the fresh rosemary in the oil, then pat on top of steaks, repeat to add extra flavor to steaks.
Let steaks rest for 5 minutes before cutting. Serve steaks with mushrooms. Enjoy.