Thinly slice the white and light green parts of the leeks. Rinse well. Thinly slice your celery.
Warm 1 tbsp oil in a pan over a medium heat. Add the veg and season well. Lower the heat. Fry for a few mins, stirring often.
Peel, core and finely dice your apple. Fold the apple and 2 tsp fennel seeds in with the veg. Sizzle till the apple starts to break down and caramelise.
Drain and rinse the beans. Finely chop 3 sage leaves. Pluck out a few flat, pretty sage leaves and set aside for later.
Add the chopped sage and 750ml stock (homemade or using your stock cube). Simmer till the pan starts steaming. Blend till smooth. Add a little more water, if needed, till it’s the right consistency for you. Season to taste.
Set a small frying pan over a high heat. Add 1 tbsp oil to the pan. Fry the reserved sage leaves with a pinch of salt till golden and crisp. Scatter over the soup as a garnish.