01 -
Preheat oven to 350°F. Line an 8×8-inch baking pan with parchment paper.
02 -
In a mixing bowl, beat together softened butter, granulated sugar, and brown sugar until light and fluffy.
03 -
Add egg and vanilla extract to the mixture and beat until well combined.
04 -
In a separate bowl, whisk together all-purpose flour, baking powder, salt, ground cinnamon, and ground nutmeg.
05 -
Gradually add the dry ingredients to the wet mixture, stirring until just combined.
06 -
Gently fold in the diced apple until evenly distributed.
07 -
Evenly spread the batter into the prepared pan.
08 -
Stir together granulated sugar and ground cinnamon for the topping, then sprinkle evenly over the batter.
09 -
Bake for 25 to 30 minutes, or until the edges are golden and a toothpick inserted in the center comes out clean.
10 -
Allow bars to cool completely before cutting and serving.