1. In a large, heavy bottom pot, saute diced onion in olive oil, over medium heat until tender, about 5 minutes. Add fennel garlic and salt. Lower heat and saute until fragrant, and everything begins to soften, about 7 more minutes.  Add the celeriac, pepper, bay, thyme and stock.
2. Bring to a simmer, lower heat, cover, and continue simmering until celeriac is very tender, about 15-20 minutes.
3. Using an immersion blender, blend until silky smooth (or use a blender, blending in batches, only filling blender 1/2 full. *Remember, when blending any hot liquid, hold the blender lid down firmly with a kitchen town, filling the blender only ½ full, and start on the lowest speed, to prevent a blender explosion. Return to the pot.)
4. Warm before serving and adjust salt and pepper to taste. 
5. Garnish with a swirl of creme fraise or sour cream (optional)  and a little drizzle of parsley oil.

Parsley Oil

1. Pulse all ingredients in a blender or food processor until combined.