Preheat your oven to 350°F (175°C). Grease and flour a 9x13 inch baking pan.

In a bowl, whisk together the flour, baking powder, baking soda, and salt.

In a large bowl, cream the softened butter and granulated sugar until light and fluffy.

Add in the eggs and vanilla extract, beating well.

Gradually mix in the sour cream until combined.

Slowly add the dry ingredients to the wet mixture, stirring until just combined.

Fold in the diced apples and cinnamon.

Pour the batter into the prepared pan.

In another bowl, combine the brown sugar, oats, and a bit of cinnamon. Sprinkle this topping over the batter.

Bake for 35-40 minutes or until a toothpick inserted into the center comes out clean.

Let cool before drizzling with a sweet cinnamon apple glaze if desired.