In a large pot, melt butter and cook onions until tender. Stir in carrots and poblano pepper and toss to coat. Stir in chopped squash. Pour in chicken stock and bring to a simmer. Simmer for 30 minutes until vegetables are tender.
Puree soup with immersion blender or in blender in batches. Return to pot and stir in cream. Season to taste and garnish with sliced scallion and/or red pepper.