In a small saucepan over medium heat, warm cream until steam starts to rise. Remove from heat, add hazelnuts and let cool. Season with salt and pepper; refrigerate for 1 hour. In a small soup pot over medium heat, melt butter. Add onion and saute, stirring occasionally, until tender and translucent, 4-6 minutes. Add cups stock and squash puree and bring to a simmer, stirring; reduce heat to medium-low. Cook,stirring, 12-15 minutes. Puree with blender or stick blender, adding more stock if soup is too thick. Season with salt, pepper and nutmeg. Whisk hazelnut cream until lightly foamy. Ladle soup into 4 bowls and garnish with hazelnut cream.