1In a medium saucepan over low heat, cook and stir mushrooms in butter until browned, about 5 minutes. Remove from heat and place in a medium bowl.
2In a medium bowl, whisk together dry Italian-style salad dressing mix, tarragon vinegar, water, vegetable oil, white sugar, garlic and red pepper sauce.
3Pour the whisked mixture over the mushrooms. Cover and chill in the refrigerator at least 8 hours before serving.