Preheat oven to 350°F (175°C) and grease a 9-inch cake pan. I usually line it with parchment paper too to make removing the cake easier.
In a medium bowl, whisk together flour, baking powder, baking soda, salt, cinnamon.
In a large bowl, beat butter and sugar until fluffy. Add eggs one at a time, then mix in vanilla extract.
Gradually add dry ingredients to wet mixture, alternating with milk. Mix until just smooth.
Gently fold in chopped apples so they are evenly distributed.
Pour batter into the prepared pan, smooth the top, and bake for 45-50 minutes or until a toothpick inserted in the center comes out clean.
Cool for 10-15 minutes in the pan, then transfer to a wire rack. Serve warm or at room temperature.