1. Preheat your oven to 350°F (175°C). Grease a 9-inch round cake pan and line the bottom with parchment paper.
2. In a medium bowl, whisk together the flour, baking powder, baking soda, salt, cinnamon, and nutmeg. Set aside.
3. In a large bowl, cream together the softened butter, maple syrup, and brown sugar until light and fluffy, about 3-4 minutes.
4. Add the eggs one at a time, mixing well after each addition. Stir in the vanilla extract.
5. Gradually add the dry ingredients to the wet mixture, alternating with the buttermilk. Begin and end with the dry ingredients.
6. Gently fold in the diced apples, ensuring they’re evenly distributed throughout the batter.
7. Pour the batter into the prepared cake pan, smoothing the top with a spatula.
8. Bake for 40-45 minutes, or until a toothpick inserted into the center comes out clean. The top should be golden brown and slightly springy to the touch.
9. Allow the cake to cool in the pan for 10 minutes before transferring it to a wire rack to cool completely.

From my experience, patience is key. Letting the cake cool completely enhances its flavors and makes it easier to slice without crumbling.