Step 1: In a small saucepan, melt 1 tablespoon unsalted butter over medium heat. Add the finely chopped apples and 2 tablespoons brown sugar. Cook, stirring occasionally, until apples are tender, about 5-7 minutes.
Step 2: Stir in 1/2 teaspoon vanilla extract and 1/4 teaspoon ground cinnamon. Remove from heat and set aside to cool slightly while you prepare the blondie batter.
Step 3: Preheat your oven to 350°F (175°C). Grease and flour a 9x13 inch baking pan, or line with parchment paper leaving an overhang on the sides for easy removal.
Step 4: In a large bowl, cream together 1 cup softened unsalted butter, 1 cup granulated sugar, and 1/2 cup dark brown sugar until light and fluffy.
Step 5: Beat in the 2 large eggs one at a time, mixing well after each addition. Stir in 1 teaspoon vanilla extract.
Step 6: In a separate medium bowl, whisk together 2 cups all-purpose flour, 1 teaspoon baking powder, 1/2 teaspoon salt, and 1/2 teaspoon ground cinnamon.
Step 7: Gradually add the dry ingredients to the wet ingredients, mixing on low speed until just combined. Be careful not to overmix.
Step 8: Spread about two-thirds of the blondie batter evenly into the prepared baking pan.
Step 9: Spoon the cooled apple filling over the batter, spreading it almost to the edges.
Step 10: Carefully dollop the remaining blondie batter over the apple layer. You don't need to spread it perfectly; it will melt and spread as it bakes.
Step 11: Bake for 25-30 minutes, or until the edges are golden brown and a toothpick inserted into the center comes out with moist crumbs.
Step 12: While the blondies cool in the pan, prepare the maple glaze. In a medium bowl, whisk together 1/4 cup melted unsalted butter, 1/4 cup pure maple syrup, 2 cups sifted powdered sugar, 1/2 teaspoon vanilla extract, and 1/4 teaspoon ground cinnamon until smooth. If the glaze is too thick, add a tiny bit of milk or water (1/2 teaspoon at a time) until it reaches a drizzly consistency.
Step 13: Once the blondies have cooled completely, drizzle the maple glaze generously over the top. Allow the glaze to set for about 15-20 minutes before slicing and serving.