Pre-heat oven to 425 degrees.
Add parsnips, onions, potatoes, garlic to a roasting pan and mix well so it all is well coated with oil. Top with fresh sprigs of thyme (optional).
Bake for 40 - 45 minutes, shaking / mixing every 15 minutes to prevent sticking.
Meanwhile, cook 6 pieces of bacon until crispy and cool on a paper towel lined plate.
Once parsnips and potatoes are roasted (soft to a fork), add to a large pot and add milk and stock (chicken or vegetable) and bring to a boil.
Add a 1/4 teaspoon celery salt and 1/2 teaspoon of fresh ground pepper to pan and stir well.
Bring pot to a gentle boil.
Remove from heat and blend with an immersion blender or add to a regular blender in batches to blend or to a Vitamix to blend until creamy.
Serve with fresh minced parsley and crumbled bacon.