Cut the white portion of the leek into 1/8 inch slices and place in a bowl of water to soak for 10 minutes. Make sure the leeks are completely covered in water. Drain leeks and rinse again, if needed, to ensure any sand is removed. Return pan to medium heat. Add leeks and sauté for 6-8 minutes until translucent and soft, but not brown. Stir occasionally with a wooden spoon, breaking the leeks apart from their circle shape. When leeks are soft and just turning golden, add thyme, olives, salt and pepper. Gently mix until combined.