Preheat oven to 350 degrees. In a shallow roasting pan on the stovetop, heat olive oil over medium heat. Add squash, season with salt and pepper and toss gently. Add 1/2 c of the stock and transfer the pan to the oven. Bake for 15 minutes, or until squash is just tender; do not over cook. Meanwhile, in a large nonstick skillet, heat butter oven medium heat. Add carrots, parsnips, sugar and salt and pepper to taste; cook until the vegetables are lightly browned, about 3 minutes. Add 1/2 c of the stock, cover the pan and simmer until tender, about 10 minutes. Transfer to a dish and set aside. Add leeks and the remaining 1/4 c stock to the skillet, season with salt and pepper, cover the pan and simmer until tender, about 10 minutes. Add the reserved squash, carrots and parsnips and toss gently. Taste and adjust seasonings, adding a grating of nutmeg. Simmer for an additional 3 to 4 minutes to warm through before serving.