Melt the butter in a large saucepan or in a Dutch oven over medium-high heat.
Add the onion and cook, stirring often, until softened, about 4 minutes. Add the garlic and cook an additional 30 seconds. Add the cajun seasoning, red pepper and cayenne pepper and cook 30 seconds more.
Add the pumpkin puree and the chicken broth. Stir until smooth. Bring to a boil, then reduce the heat and simmer for 10-15 minutes.
Transfer the soup, in batches, to a blender or food processor. Cover tightly and blend until smooth. Return the soup to the pan.
With the heat on low, add the brown sugar and stir until dissolved. Slowly add in the milk, whisking constantly. Taste, and adjust seasonings to taste.
Top each serving with a tablespoon of cream and pepitas, if desired.
Notes
Nutrition information provided as an estimate only. Various brands and products can change the counts. Any nutritional information should only be used as a general guideline. Nutritional information does not include pepitas.