Grease a 10-inch springform pan or 9x13x2-inch baking pan; set aside.
Stir together flour, baking powder, baking soda, 1 teaspoon ground cinnamon, and the nutmeg.
In a large separate bowl, beat the butter for until smooth with a hand mixer for about 1 minute. Add 1¼ cups of granulated sugar and vanilla, then beat until well combined. Add the eggs, one at a time, beating well after each addition.
In a separate bowl, stir the mashed squash with the buttermilk. Add squash mixture and dry ingredients alternately to the egg mixture and mix thoroughly.
Add 1½ cups of the chopped apple, walnuts, and the raisins into the batter. Spoon the batter into the prepared pan. To the remaining 1 cup of chopped apples, add the remaining ½ cup granulated sugar and ½ teaspoon of cinnamon and toss well to coat the apples. Scatter the cinnamon sugar apples on top of batter.
Bake in 325°F oven for 1 to 1¼ hours for springform pan, and 50 minutes to hour for 9x13-inch pan or till cake tests done with a toothpick. Cool on rack for 10 minutes. If using springform pan, loosen sides of pan; if using a 9x13 baking pan, invert onto cooling rack after 10 minutes. Allow to cool completely before either glazing or frosting.