Warm the olive oil in a large soup pot or Dutch oven over medium heat. Add the onion, salt, and a few generous grinds of black pepper. Cook, stirring occasionally, until the onion is soft and translucent, 5 to 8 minutes.

Stir in the cubed butternut squash and cook for 8 to 10 minutes, stirring occasionally, until the squash begins to soften. Add the garlic, sage, rosemary, and ginger and cook for 30 seconds to 1 minute, until fragrant. Pour in 3 cups of the broth, raise the heat to high, and bring to a boil. Once boiling, cover the pot, reduce the heat to a gentle simmer, and cook until the squash is completely tender, 20 to 30 minutes.

Let the soup cool slightly, then puree it in batches in a blender until completely smooth. If the soup looks too thick, add the remaining cup of broth and blend again. Taste and adjust the seasoning with salt and pepper, then serve warm with parsley, pepitas, and sourdough bread.