Melt butter in large heavy-bottomed saucepan. Add onion; sauté until softened, 2 minutes. Add apples, broccoli, chicken broth, salt, pepper and nutmeg. Simmer until broccoli is tender, about 18 minutes.
Remove from heat. Stir in lemon juice and hot-pepper sauce. Let mixture cool slightly.
In batches, puree mixture in blender. Return to pan; reheat to simmering. Just before serving, stir in sour cream. Garnish with unpeeled apple slices or dice if desired.