Cream butter in small bowl using a fork or electric mixer and gradually blend in other ingredients. Butter mixture can be used while still soft; or it can be rolled into a cylinder in parchment paper or plastic wrap and refrigerated or frozen, then sliced into teaspoon-sized rounds. Flavored butter can be stored a couple days in the refrigerator or it can be frozen for several weeks.
Season steaks with salt and pepper.
Heat a large cast-iron skillet or pan over medium-high heat. Add 1 tablespoon of oil and swirl to coat. When oil is shimmering, lay the steaks in pan and cook without moving until well browned, about 3 to 5 minutes. Flip steaks and add 1 Tablespoon of flavored butter to the top of each steak. Cook for another 3 to 5 minutes or until desired doneness.
Remove the steaks and let rest. Add the balsamic vinegar to the pan and scrape any brown bits. Add the mushrooms to the pan and sauté on medium heat until soft.
Pour mushrooms and pan sauce onto steaks and serve.