In a pot over medium high heat, add the butter and olive oil. Cut the fresh steak into 1 inch cubes and season with salt. Sear all sides and then remove from the pot. Set cooked steak aside.
In the same pot over medium heat, add diced onion. Cook until the onion is browned and softened. Add in the garlic, herbs, and mushrooms. Cook until the mushrooms are browned and soft.