Prep leeks, garlic and celeriac as noted. Press the "Sauté" button on the Instant Pot and add avocado oil. Once hot, add the leek and garlic and cook, stirring occasionally for 3-4 minutes.
Press the "Cancel/Keep Warm" button, and add the celeriac, thyme, salt and pepper. Stir to mix and then add in the broth.
Secure the lid on the Instant Pot and close the pressure valve. Press the “Manual” button or "Pressure Cook" and cook on high pressure for 5 minutes.
When the soup is done cooking, quick release the pressure. Blend the contents of the Instant Pot to a smooth consistency with an immersion blender (or carefully transfer contents to a blender and blend).
Add in the lemon juice and stir. Taste and season with salt and pepper as desired. Ladle into bowls and serve, topping with chopped thyme and optional toppings as desired.
For the stove top:
Prep leeks, garlic and celeriac as noted. Heat a large stock pot over medium heat and add avocado oil. Once hot, add the leek and garlic and cook, stirring occasionally for 3-4 minutes.
Add in the celeriac, thyme, salt and pepper. Stir to mix and then add in the broth. Bring to a quick boil and then lower heat to medium-low. Cover and simmer for 10-15 minutes, or until the celeriac cubes are softened.
When the celeriac cubes are soft, blend the contents to a smooth consistency with an immersion blender (or carefully transfer contents to a blender and blend).
Add in the lemon juice and stir. Taste and season with salt and pepper as desired. Ladle into bowls and serve, topping with chopped thyme and optional toppings as desired.