In a large pot, combine the cubed butternut squash, chopped onion, chopped carrots, and chicken broth.

Heat the pot over medium heat until the soup begins to simmer. Once it's simmering, let it cook uncovered for about 45 minutes, or until the vegetables are very soft and tender.

Carefully remove the pot from the heat. Using an immersion blender, blend the soup directly in the pot until it's completely smooth. If you don't have an immersion blender, you can carefully transfer the soup to a regular blender in small batches to puree it, then pour it back into the pot.

Return the pot to the stove over low heat. Stir in the butter until it has melted, then pour in the whipping cream. Stir until everything is well combined and the soup is creamy.

Season the soup with salt to taste.

Serve the soup hot, topped with a dollop of sour cream or a sprinkle of black pepper, cinnamon, or brown sugar if you like! To get the fun swirl garnish, for one bowl of soup, in a small bowl mix 1 Tablespoon of sour cream with 1 teaspoon of milk or water. Whisk until loose and smooth. Spoon mixture onto one side of the soup surface and run a chopstick or fork through into a spiral pattern.