Heat a large saute pan over medium heat with two tablespoons of olive oil. Add the butter and let it melt, stirring frequently. As the butter begins to brown, add the sage and continue to stir. Cook the sage leaves for about a minute, until the sage wilts and releases its fragrance. Pull the sage leaves out. Add the 4 cloves of pressed garlic, butternut squash and sherry. Season with salt and pepper. Cook over medium heat, covered for 30 to 40 minutes or until the squash is fork tender. Stir periodically while it cooks. When squash is tender, add mushrooms and stir. Season with salt and pepper. Cook for two to three minutes, then add the kale. Season with salt and pepper. Stir continuously when kale is added until the kale is cooked down to less than half the initial volume. Finish by stirring in cooked spaghetti, cheeses and walnuts.