Prepare the Oven and Pan:
Preheat your oven to 350°F (175°C). Grease and flour a 9-inch round cake pan or line it with parchment paper.

Mix the Dry Ingredients:
In a large bowl, whisk together flour, baking powder, baking soda, cinnamon, nutmeg, and salt. Set aside.

Cream Butter and Sugar:
In another bowl, cream together the butter and granulated sugar until light and fluffy, about 3-4 minutes. Add the eggs, one at a time, mixing well after each addition. Stir in the vanilla extract.

Combine Wet and Dry Ingredients:
Gradually add the dry ingredients to the wet ingredients, alternating with the buttermilk. Mix until just combined.

Add Apples:
Gently fold in the chopped apples until evenly distributed throughout the batter.

Transfer to Pan and Add Topping (Optional):
Pour the batter into the prepared cake pan. If desired, sprinkle the top with brown sugar and dot with small pieces of butter for a sweet, caramelized topping.

Bake the Cake:
Bake in the preheated oven for 45-55 minutes, or until a toothpick inserted into the center comes out clean. Let the cake cool in the pan for about 10 minutes, then transfer to a wire rack to cool completely.

Serve:
Dust the cooled cake with powdered sugar (optional) and serve. Enjoy with whipped cream or custard if desired.