Wash outside of squash thoroughly, keeping the skin on the squash. Chop squash into 8 pieces, set aside seeds and string.
In a large soup pot melt, 1 tbsp butter over medium heat, stir in leeks and cook until softened. Add seeds and strings and cook for 5 more minutes, stirring often. Add water and squash pieces, bring to a boil.
Cover, lower heat and cook for 30 - 40 minutes until squash meat can be easily pierced with a fork. Remove squash from the pot and allow to cool slightly. Separate the squash from the peel, discard the peel and put squash into a blender. Strain the remaining cooking liquid and add to the blender. Puree the broth and squash until it is very creamy. Return the puree to the pot, add chicken broth, mix well and bring to a simmer. 
In the meantime, warm the olive oil in a 12" skillet over medium heat. When the oil is hot, toss in the sage leaves and quickly fry. Drain the leaves on paper towels. 

Before serving the soup, stir in 1/4 cup of half and half. Serve warm with 2 - 3 leaves on top of each bowl.