Beef Tenderloin with Marsala without cocoa

4 tablespoons butter 2 tablespoons olive oil 14 ounces white button mushrooms , sliced (can use more) 2 -3 tablespoons shallots , finely chopped (or to taste)[...]

2 tablespoons olive oil 3 tablespoons balsamic vinegar 1 (1 1/2-2 lb) beef tenderloin 1 1/2 tablespoons white peppercorns 1 1/2 tablespoons black peppercorns[...]

3 tablespoons balsamic vinegar (or 2 tablespoons red wine vinegar plus 1 1/2 teaspoons sugar) 2 tablespoons olive oil 1 (1 1/2-2 lb) center-cut boneless beef[...]