In large bowl, beat 3/4 cup butter and the granulated sugar with electric mixer on medium speed until light and fluffy. Beat in eggs until fluffy. Beat in baking powder, baking soda, salt, ginger, cinnamon and nutmeg. Add flour alternately with buttermilk, scraping side of bowl. Beat 1 minute. Stir in squash and 1/2 cup walnuts. Spread in pan.