You can find this exercise on page 299 of the book Synergistic Golf.
Exercise Type: YOGA-STRETCH
Exercise Category: FLEXIBILITY, HIPS, LEGS - FEET, LOW BACK
Stand with feet wider than hip distance apart and toes aiming outward at 45 degree angle. Squat down keeping weight in heels and rest elbows on thighs. Try to hold position for approximately 10-15 seconds then repeat. For extra stretch, place hands on floor inside feet and prop elbows on inside of knees. Breath slowly through stretch allowing muscles to give in to gravity and experience full stretch.