Preheat the oven to 350°F (175°C).
Prepare a 9-inch round cake pan with butter and flour.
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.
In a separate bowl, whisk together the flour, baking powder, baking soda, salt, and cinnamon.
Gradually mix the dry ingredients into the butter mixture until just combined.
Fold in the sliced apples gently until evenly distributed.
Pour the batter into the prepared cake pan and smooth the top.
Bake for 45–50 minutes or until a toothpick inserted into the center comes out clean.
Allow the cake to cool in the pan for 10 minutes before transferring to a wire rack.
Serve warm with a dusting of powdered sugar or a dollop of whipped cream, if desired.