Roast Beef Tenderloin with Sautéed Mushrooms

Name: Roast Beef Tenderloin with Sautéed Mushrooms
Ingredients: 1 3/4 to 2 pound section beef tenderloin (preferably a piece cut from the center), trimmed of excess fat and silverskin; 1 teaspoon kosher salt; 1/2 teaspoon coarsely ground black pepper; 1 1/2 tablespoons extra virgin olive oil; 1 pound cremini mushrooms, sliced 1/8 to 1/4 inch thick; 3 tablespoons butter; 1 teaspoon salt (use 1/2 teaspoon if using salted butter); 2 tablespoons minced shallots; 2 tablespoons minced garlic; 1 1/2 teaspoons Herbs de Provence or 1 teaspoon of dried tarragon