Melt the butter in a large saucepan.

Add all the vegetables, cover with a lid and cook on a low heat for 10-15 minutes to soften them.

Add the white wine, increase the heat and reduce the liquid by half in an open pan.

Add the stock, milk, lemon juice and seasoning.
Simmer for 30 minutes.

Stir in the single cream.

Fit the blender attachment.
Process the soup on speed 1 for a few seconds and then increase to speed 2 for about 15-20 seconds until smooth.

Reheat and serve with croutons.