Preheat your oven to 350°F (175°C).
Grease and flour a Bundt pan.
In a large bowl, cream together the softened butter and granulated sugar until light and fluffy.
Add the eggs one at a time, mixing well after each addition.
Stir in the vanilla extract and buttermilk until just combined.
In a separate bowl, whisk together the flour, baking soda, salt, cinnamon, and nutmeg.
Gradually add the dry ingredients to the wet mixture, mixing until just combined.
Fold in the diced apples, brown sugar, and nuts (if using).
Pour the batter into the prepared Bundt pan and smooth the top.
Bake in the preheated oven for 55-65 minutes or until a toothpick inserted into the center comes out clean.
Allow the cake to cool in the pan for 10 minutes before inverting onto a wire rack.
Dust with powdered sugar before serving, if desired.