Place olive oil and butter in the skillet and turn it up to medium-high. Wait for 30 seconds. Add shallot and cook for 1 minute or until fragrant. Place sliced mushrooms in the skillet (if the skillet is dry add more oil). Cook for 3-4 minutes or until golden. Add garlic and cook for 30 seconds or until fragrant. Add flour and stir constantly for ~30 seconds. Add beef broth, thyme, rosemary, salt, pepper and stir.
Turn down the heat to medium and cook for addtional 6-8 minutes or until the sauce has thickened to your preference.
Serve with mash potatoes, pasta or rice. Optional: top with fresh chopped parsley. Enjoy!