Cook bacon in a large saucepan over medium-high heat until crisp. Add leek; cover, reduce heat to medium-low, and cook 3 minutes. Add stock, potato, salt, and thyme; bring to a boil. Reduce heat; simmer 15 minutes or until potato is tender. Remove 1 cup potato with a slotted spoon; place in a blender. Add 1/2 cup cooking liquid to blender; process until smooth. Return puréed mixture to pan. Sprinkle with parsley.