1. In a small glass measuring cup, mix together Wasabi powder and water to form a thick paste. Allow to stand for 5 minutes. In a medium-size bowl, add Wasabi paste, mayonnaise, sour cream, lemon juice and salt. Whisk until smooth; you should have about 2 cups. Gently stir in chives. Cover and refrigerate.Steak:
2. Place tenderloin on a flat cutting surface. Cut into 3 equal round pieces, each about 3 inches in length. With a sharp slicing knife, cut each piece in a circular motion so that each piece becomes a long flat strip of steak about 1/2-inch thick. Pound the meat slightly.
3. Place steak, olive oil and garlic into a large resealable bag. Marinate at room temperature for 30 minutes.
4. Heat gas grill to high or prepare charcoal grill with hot coals. Shake excess marinade off steak and grill about 1-1/2 to 2 minutes per side for medium-rare or until internal temperature reaches 135 degrees F on an instant-read thermometer. Remove from heat and allow to rest 5 minutes in a warm place. Slice and serve immediately with the Wasabi sauce. Makes 8 servings.