Cover parsnips and potatoes with water, bring to boil, salt water and cook to very tender. Drain and mash well.
Meanwhile, heat a soup pot over medium heat with a drizzle of EVOO. Add bacon and brown; add onions, celery, marjoram, bay, ginger, a little pepper, vinegar, brown sugar and cook until very soft.
Add mashed parsnips and potatoes to soup pot and stir to combine with stock; add water to thin if soup is too thick. Adjust salt and pepper, to taste, and stir in parsley. For a smooth soup, purée with a hand blender then garnish with parsley.