01 -
Preheat oven to 350°F (175°C). Line a 9x9 inch baking pan with parchment paper. In a light-colored saucepan, melt the butter over medium heat. Continue to cook, swirling the pan occasionally, until the butter foams, and then subsides, and brown specks appear at the bottom. It will smell nutty. Immediately pour the browned butter into a large mixing bowl to cool for 5-10 minutes.
02 -
Once the butter has cooled slightly, add the packed brown sugar to the bowl and whisk until well combined. Add the egg and vanilla extract and whisk again until smooth and glossy.
03 -
In a separate medium bowl, whisk together the flour, baking powder, salt, cinnamon, and nutmeg.
04 -
Pour the dry ingredients into the wet ingredients and fold together with a rubber spatula until just combined. Do not overmix; a few streaks of flour remaining is okay.
05 -
Gently fold in the chopped apples. Spread the thick batter evenly into the prepared pan. Bake for 28-32 minutes, or until the edges are golden brown and a toothpick inserted into the center comes out with moist crumbs attached.
06 -
Remove from the oven and let the blondies cool completely in the pan on a wire rack. This is crucial for the texture and to ensure the frosting doesn't melt.
07 -
While the blondies cool, prepare the frosting. In a mixing bowl, beat the softened cream cheese and softened butter with an electric mixer until smooth and creamy. Gradually add the powdered sugar and beat until combined. Add the vanilla and pinch of salt, and beat until light and fluffy.
08 -
Once the blondies are completely cool, spread the cream cheese frosting evenly over the top. Use the parchment paper overhangs to lift the blondies out of the pan. Cut into squares and serve. Sprinkle with flaky sea salt, if desired.