Place a large pot over medium heat and add oil to the pan.
Add in the ground beef and chopped onion and cook while breaking it up with a wooden spoon until browned, about 5 minutes. Add in the carrots, celery, parsnips, potatoes, rosemary, thyme and 4 cups chicken broth and bring to a boil.
Cover, reduce to a simmer and cook for 20 minutes or until all of the veggies are fork tender.
Scoop out 1 cup of the potatoes and add them to a blender with remaining 1 cup of chicken broth. Blend on high until smooth, then pour that back into the pot of soup.