Melt 4 tablespoons butter in Dutch over medium heat. Stir in celery, carrots, onions. Cover pot and reduce heat to low. Let vegetables cook for 30 minutes. Remove the lid. Add potatoes and chicken stock and simmer 30 minutes until tender. Stir in cream and sea salt.
In a small saucepan melt remaining 4 Tbs. butter and add 1/2 cup of flour or 1/4 cup arrowroot (whisking while incorporating to avoid clumping). Let the butter and flour mixture cook for a couple of minutes while constantly stirring. Stir the flour mixture into the vegetables and broth. Blend soup until creamy using a hand immersion blender or you can blend the soup in a blender in small batches. Adjust sea salt to taste. Garnish with cheese and sour cream, green onions and pepper.