Preheat oven to 350°F (175°C). Grease and line a 9×13-inch baking dish with parchment paper.
- In a medium bowl, whisk together flour, baking powder, salt, and cinnamon.
- In a large bowl, whisk melted butter with brown sugar and granulated sugar until smooth.
- Add eggs and vanilla extract, mixing until fully combined.
- Gradually add dry ingredients to wet mixture, stirring until a thick batter forms.
- Fold in chopped apples until evenly distributed.
- Spread batter evenly in the prepared baking dish and smooth the top.
- Bake for 30–35 minutes, or until edges are golden and a toothpick comes out clean.
- While brownies cool slightly, prepare the glaze by whisking powdered sugar, maple syrup, and milk or cream until smooth. Stir in melted butter and salt if using.
- Drizzle glaze over warm brownies. Cool completely before slicing into bars.