Melt the butter in a large pot over medium heat. Stir in the onion, garlic, curry powder, and red pepper flakes. Cook until the onion has turned translucent, 5 to 8 minutes.
Stir the chicken stock and squash into the onion mixture. Simmer the soup over medium heat until the squash is tender when pierced with a fork, about 20 minutes. Turn off the heat, and stir in the nutmeg, Worcestershire sauce, and peanut butter.
Transfer the mixture in batches to a blender or food processor; blend until smooth, slowly pouring in the cream. Reheat soup if necessary, but do not boil.