Preheat the oven to 350°F (175°C). Grease and flour a 9-inch cake pan.
In a bowl, whisk together flour, baking powder, baking soda, and salt.
In a separate bowl, cream together butter and sugar until fluffy.
Beat in eggs and vanilla extract until smooth.
Gradually add the dry ingredients, alternating with the buttermilk, mixing until just combined.
Gently fold in the chopped apples.
Pour the batter into the prepared pan.
In a small bowl, mix sugar and cinnamon, then sprinkle it over the batter.
Bake for 40 minutes, or until a toothpick inserted in the center comes out clean.