In a large skillet over medium heat, melt butter. When butter is hot, add sage leaves and cook until they turn a different shade of green and are crisp. Transfer sage leaves to a paper towel to drain excess butter.
Cook butter until it is browned and fragrant, then add squash noodles and salt. Cook, stirring, until noodles are softened but still firm for about 4 minutes.
Add cream and cook until noodles are lightly coated.
Garnish noodles with fried sage and walnuts.