In a large sauce pan or soup pot, heat butter over medium heat. When melted, add onion and sauté until translucent. Add garlic and stir fry from 2 minutes, until fragrant. Add potatoes and pumpkin, and cook for 4 minutes. Add vegetable stock and dried beans and bring to a boil. Cover and cook for 25 to 30 minutes until pumpkin and potatoes are tender.
Using a blender, or stick blender, puree soup until smooth. Return to heat, add cannellini beans and simmer for 1 to 2 hours until beans are tender. Add additional stock if soup thickens too much.
Remove from heat. Add cream and stir to combine. Add a bit more stock if needed to reach desired consistency. Add ginger, lemon juice, nutmeg, bacon and sage leaves. Stir into soup. Season with salt and pepper to taste. Serves 4 to 6.