In a spacious Dutch oven or a heavy-bottomed pot, melt the unsalted butter over medium heat. Introduce the finely chopped onions, carrots, garlic, and ginger, seasoning them with kosher salt and freshly ground pepper. Cover the pot and cook, stirring occasionally, until the vegetables become tender, approximately 5 to 6 minutes.
Add the peeled and cubed butternut squash to the pot, cover, and cook, stirring occasionally, until the squash is just fork-tender, about 4 to 5 minutes. Stir in the tomato paste and smoked paprika, cooking for an additional 1 to 2 minutes until the tomato paste deepens in color.
Incorporate the pumpkin puree along with 6 cups of vegetable broth into the mixture. Partially cover the pot and bring the contents to a boil over high heat. Once boiling, reduce the heat to medium-low and let the soup simmer, stirring occasionally, until the squash is very tender, roughly 15 minutes.
Remove the pot from the heat. Using an immersion blender, blend the soup until it reaches a smooth consistency. Alternatively, allow the soup to cool slightly and blend in batches using a standard blender. If the soup is too thick, add more broth incrementally, about 1/4 cup at a time, until the desired consistency is achieved. Season with additional salt and pepper to taste.
Ladle the soup into bowls and, if desired, top with a dollop of heavy cream or sour cream, along with roasted pumpkin seeds for an added crunch.