To prepare the asparagus cut the tough woody ends from the stems and discard.

Cut the asparagus tips from the stems and slice them in half lengthways .Heat the water in the casserole and when simmering add the tips, place on the lid and cook for 3 - 4 minutes until they are tender. Remove the tips and pour the cooking water into a jug.

Cut the main part of the asparagus stems into 2½cm (1inch) lengths.

On the hob, heat the butter in the casserole over a medium heat, add the chopped onions with the diced potatoes and stir fry for 4 - 5 minutes.

Add the cut asparagus stems, vegetable stock, reserved cooking water and black pepper. Bring to a simmer and cook for 6 - 8 minutes until the vegetables are tender.

Decant the contents of the casserole into a food processor or large blender and pulse until smooth.

Return the blended mixture to the casserole stir in the cooked asparagus tips, 150ml (5floz) of the crème fraîche and adjust the seasoning to taste.

Heat the soup to piping hot and serve with the remaining crème fraîche swirled through and a sprinkle of black pepper.

To make the croutons; cut 3 - 4 slices of white or wholemeal bread into cubes, heat 1 tablespoon butter with 2 tablespoons of olive oil in a frying pan, stir fry the bread until golden and crisp, sprinkle with a little sea salt and some chopped fresh parsley. Sprinkle on top of the soup.

Cook's Notes

As the soup is blended more of the stem can be used than when eaten as a vegetable.

Using crème fraiche rather than cream gives the soup a fresher taste.