Melt the butter in a heavy saucepan over medium heat. Add the onions. Cook, stirring, until translucent. Add the pumpkin and stir in the milk or half-and-half until blended. Add the red pepper flakes, curry powder and ginger. Remove from heat. Blend or process the mixture in a food processor until smooth. Return the mixture to the pan and add the chicken broth. Heat thoroughly, but do not boil. Serve with a dollop of Mexican cream. Add a tiny sprig of green garnish beside the cream.