Place all the butter for the blondies and icing in a light-colored skillet over medium heat. Stir frequently while it melts and begins to foam.

Continue cooking for about 5–8 minutes, watching carefully. When golden-brown specks develop on the bottom and the butter smells toasted and nutty, immediately remove the skillet from the heat.

Pour the browned butter, including the flavorful browned milk solids, into a heat-safe container. Reserve about 3 tablespoons (43g) for the icing. Let the remaining butter cool slightly.

Return the skillet to medium heat. Add the chopped apples, maple syrup, and cinnamon. Cook for 3–5 minutes, stirring occasionally, until the apples begin to soften. Remove from the heat and set aside.

Preheat the oven to 350°F (177°C). Line a 9×13-inch baking pan with parchment paper, leaving enough overhang to lift the finished blondies from the pan.

Whisk the flour, baking powder, salt, cinnamon, and nutmeg together in a large mixing bowl.

In a separate bowl, whisk the browned butter with the brown sugar, eggs, and vanilla until well combined.

Add the wet mixture to the dry ingredients. Stir just until a thick batter forms, then gently fold in the cooked apples. Avoid overmixing your Brown Butter Apple Blondies, as this helps preserve their soft, chewy texture.

Spread the batter evenly in the prepared baking pan. Bake for approximately 35 minutes, or until the surface is lightly golden and a toothpick inserted into the center comes out mostly clean with a few moist crumbs.

Place the pan on a cooling rack and allow the blondies to cool completely before icing.

To prepare the icing, gently warm the reserved browned butter if it has solidified. Whisk it with the confectioners’ sugar, milk, vanilla, and salt until smooth. Add a little extra milk if necessary for a thinner consistency.

Spread or drizzle the icing over the cooled blondies. Use the parchment overhang to lift them from the pan, then slice into squares and serve.