Preheat your oven to 350°F (175°C). Grease and flour a 9x13 inch pan.
In a large bowl, cream the butter and sugar together until smooth.
Stir in the eggs and vanilla extract until well combined.
In another bowl, sift together the flour, baking powder, baking soda, salt, and cinnamon.
Gradually add the dry ingredients to the wet ingredients, mixing until just combined.
Fold in the diced apples.
Spread the batter into the prepared pan.
Bake for 45 minutes or until a toothpick inserted into the center comes out clean.
Allow the cake to cool before serving.