Peel the butternut squash, cut it into pieces and collect it in a saucepan with the extra virgin olive oil and the thinly sliced leek. Cook the leeks and squash over low heat for about 25 minutes, stirring often to flavor the pumpkin and to prevent the leek from burning.
Pour in the water and the chickpeas and cook for 15 more minutes, stirring occasionally, then blend everything. Season with salt and pepper and add a pinch of grated nutmeg.
In a saucepan melt the butter with the sage leaves and cook until they are crisp.
Serve the soup topped with the crisp sage leaves and drizzle with the brown butter.