Heat the olive oil in a large pot on medium heat. Add in the onion and cook for a few minutes until it begins to soften.
Add in the cubed apple, celeriac, thyme, salt and 2 cups of the vegetable stock and let simmer for 20 minutes until the celeriac is soft.
Transfer everything from the pot into a blender and blend or alternatively use a hand emulsifier to puree everything in the pot. Once smooth return the mixture to the pot and add in the remaining 1 cup vegetable stock and almond milk. Stir and bring to a boil. Taste and adjust seasoning with more salt, thyme or vegetable stock if too thick.
In a bowl combine the chopped walnuts and thyme and mix
Serve the soup topped with the walnuts and thyme.