You can find this exercise on page 113 of the book Synergistic Golf.
Exercise Type: YOGA-STRETCH
Exercise Category: FLEXIBILITY, HIPS, LEGS - FEET, LOW BACK
Sit on floor with your legs outstretched and knees slightly bent. Lift your left calf and cross it over your right thigh, placing the left foot flat on the floor next to the right leg. Sit up tall and rotate your shoulders and head as far left as is comfortable, keeping your shoulders relaxed. Hold for 10-30 seconds each side. You may reach opposite arm across body and press slightly on outside of knee for increased stretch.