Heat butter in large saucepan over medium heat. Add chopped onion and sauté 5 minutes or until softened but not browned.
Stir in curry powder and crushed red-pepper flakes. Add Granny Smith apples and continue cooking for 10 minutes longer.
Add solid-pack pumpkin, chicken broth and 1/2 cup water; stir to combine. Cook 5 minutes. Remove from heat.
Puree in a blender or food processor until smooth, working in batches.
Return to saucepan. Bring to boiling. Lower heat as soon as the soup reaches boiling. Simmer 2 to 3 minutes to blend flavors. Just before serving, stir in half-and-half or heavy cream. Makes 6 servings.