Whisk together the flour, baking powder, baking soda, cinnamon, nutmeg and salt in a bowl. Cream butter, sugar and eggs with a mixer. Combine with flour, add buttermilk and vanilla and mix. Fold in chopped apples and nuts with a spoon. Spray or line a 10 x 15 jelly roll pan (this is a regular baking sheet with a lip all the way round it)I usually just line mine with aluminum foil.Spread cake mixture in pan. Bake in a preheated 350 degree oven for 25 to 30 minutes. Let cool and frost