Using an electric mixer, beat the butter at high speed until fluffy. Gradually beat in the sugar. Add the eggs, 1 at a time, beating between additions. Beat in the vanilla. At low speed, beat in the flour mixture, alternating with the Squash Puree and buttermilk. Scrape the batter into the prepared pan and smooth the top. Bake for 55 minutes, or until a toothpick comes out clean. Let the cake cool in the pan for 15 minutes. Turn it out onto a rack, then invert and let cool completely.