Preheat over to 375 degrees F. Grease and flour a 13 x 9 pan, or if you want a layer cake, prepare two 9-inch round pans.
Melt the chocolate and oil in a small saucepan over very low heat. Cream butter until light; add the sugar, eggs and vanilla. Beat well. Add the melted and cooled chcolate mixture and mix well. Sift or stir together the dry ingredients and stir them into the batter with the buttermilk. Mix the squash and nuts into the batter.
Bake 13 x 9 cake for 40-45 minute and 9-inch pans for 35-40 min., or until a toothpick inserted into the center comes out clean.
Cool the cake completely before frosting with whipped cream or your favorite frosting. Try this frosting:.
3/4 cup butter at room temp., 8 oz. cream cheese at room temp., 4 plus cups confectioner's sugar, and 1 teaspoon vanilla. Cream butter and cheese together until the mixture is light and fluffy. Add vanilla. Slowly add the confectioner's sugar until well blended, using more sugar if necessary to get a spreading consistency. Best stored in fridge.