Preheat the oven to 350°F (175°C).
Grease and flour a Bundt pan.
In a large mixing bowl, whisk together the flour, baking powder, baking soda, salt, cinnamon, and nutmeg.
In another bowl, cream the softened butter and granulated sugar until light and fluffy.
Add the eggs, one at a time, mixing well after each addition, then stir in the vanilla extract.
Gradually add the dry ingredients to the wet mixture, alternating with the diced apples, stirring until just combined.
Fold in the chopped nuts, if using.
Pour the batter into the prepared Bundt pan, smoothing the top with a spatula.
Bake for 55-60 minutes or until a toothpick inserted into the center comes out clean.
Allow the cake to cool in the pan for 15-20 minutes before inverting onto a wire rack to cool completely.
While the cake cools, prepare the glaze by whisking together powdered sugar and milk until smooth and pourable.
Once the cake is completely cool, drizzle the glaze over the top and allow it to set.