Cut enough florets to measure 2 cups. Cut rest of broccoli into 1- in.pieces. Cook florets and broccoli pieces, separately, in lightly salted water until just tender. (Florets will be done first). Immediately rinse in cold water. Drain. Set florets aside until serving time.
In a large saucepan saute leeks in butter until tender; usually about 4 minutes. Sprinkle in flour and cook one more minute, stirring with whisk. Remove from heat and stir in broth. Return to heat and simmer for 5 minutes, stirring occasionally. Add broccoli pieces to broth and puree in blender in batches, until smooth. Just before serving, blend in cream and Swiss cheese. Simmer gently until cheese melts. Add nutmeg, salt, pepper. Add reserved florets and heat through.