In the bowl of a stand mixer fitted with the paddle attachment, cream the butter and sugar until pale and fluffy, about 2 minutes.
Add the vanilla and egg to the mixer and beat well.
With the mixer on low, alternately add the dry ingredients and buttermilk in 3 additions, starting and ending with the dry ingredients (so dry, buttermilk, dry, buttermilk, dry).
Beat only until just combined.
Scrape the batter into the cake pan, smoothing the top with a rubber spatula. Scatter the apple pieces evenly over the top of the cake batter then sprinkle evenly with raw sugar. Finally, sprinkle lightly with cinnamon.
Bake for 25-30 minutes, or until the cake is golden and a toothpick inserted in the center comes out clean. Let the cake cool in the pan for ten minutes, then turn it onto a wire rack to cool.