Add the bread to a bowl and stir in the olive oil, sage and garlic until fully combined.
Place the bread on a baking tray and bake in the oven or place under the grill until they toast and become crispy.
Set them to one side while you make the soup.
Add the onion and garlic to a pan and cook gently for 5 minutes until beginning the soften.
Add the celeriac and apple to the pan, cover with a lid and cook gently for a further 5 minutes.
Add the stock and seasoning and bring to the boil
Simmer for 10 minutes until the celeriac is soft.
Use a hand blender to blend the soup until smooth.