Remove the leaves from the celery, if any, and wash them. Wash the celery root thoroughly. Scrub off any dirt. Peel the celery root, cut it into large pieces, and set aside.
Peel, remove the root end, and quarter the onion. Make a bouquet garni with a bay leaf and a few sprigs of thyme. Prepare a rich vegetable broth.
The Chef’s Tip
If you’re using a bouillon cube, squeeze the cube well at the end to extract all the flavor.
Bring the vegetable broth and hazelnut drink to a boil. Add the bouquet garni, onion, celery pieces, and half of the celery leaves. Season withsalt and pepper to taste, then simmer, covered, for about 25 minutes.
Preparing the hazelnut filling
Preheat the oven to 150°C (300°F). While the soup is cooking, toast the hazelnuts in the oven for about 20 minutes.
Grate the orange zest and squeeze the orange to extract the juice. Once roasted , chop the hazelnuts in a food processor. Chop the other half of the greens.
Combine the chopped hazelnuts with the flaxseed oil, chopped chives and parsley, and the juice and grated zest. Season this hazelnut topping with salt and pepper.
Blending and serving
Check that the celery pieces are cooked, turn off the heat, and remove the bouquet garni. Blend the soup until it has a smooth consistency.
Adjust the seasoning of the soup and serve it hot with a spoonful of hazelnut topping.