
In a large stockpot over medium heat, melt butter and oil. Add the onion and stir until translucent, about 5 minutes. Add the chicken broth and bring to a simmer.
Add the butternut squash cubes, orange juice, and orange zest. Bring to a boil, reduce heat, and simmer until the squash is tender, about 20-25 minutes. Remove from heat.
Using an immersion blender, puree the soup until smooth. Whish in sour cream (or yogurt) and season with salt and pepper. Reheat over low heat until warmed up again and serve hot.