Preparation
Remove the tough stems and leaves from the broccoli. Cut off the stalks, peel and cut into 1 inch pieces. Break the florets into very small pieces and set aside.
Melt the butter in a large saucepan. Add the onion and broccoli stalks and cook, covered, for 5 minutes over a moderate heat. Stir often.
Add the reserved broccoli florets, potato and stock to the pan. Bring to a boil and cook, partially covered for 25 minutes, or until all the vegetables are soft.
Using a blender or food processor, puree the mixture in batches until smooth, transferring each batch to a clean saucepan. Add the cream, lemon juice and Worcestershire sauce to the pan. Simmer for 3-5 minutes, but do not allow to boil or the soup will curdle.
Just before serving, stir in the grated cheese.