In a medium light-colored skillet, melt 1 cup unsalted butter over medium heat. Swirl occasionally as it foams and sizzles. After 5 to 7 minutes, nutty golden-brown specks will form on the bottom. Immediately pour into a heatproof bowl to cool for 10 minutes.

In a small skillet, melt 1 tablespoon butter over medium heat. Add diced apples, 2 tablespoons brown sugar, 1 teaspoon cinnamon, and nutmeg. Sauté for 4 to 5 minutes until apples are just tender and excess juices evaporate. Remove from heat and cool completely (this ensures blondies don't become soggy!).

Preheat oven to 350°F (175°C). Line an 8x8-inch or 9x9-inch square metal baking pan with parchment paper, leaving an overhang on the sides.

In a large bowl, vigorously whisk cooled brown butter with brown sugar and granulated sugar for 2 full minutes until glossy and combined.

Whisk in eggs, egg yolk, and vanilla extract vigorously for 1 minute until batter turns thick and pale—this step forms the crinkly, paper-thin shiny crust!

Gently fold in flour, baking powder, sea salt, and ½ teaspoon cinnamon with a rubber spatula just until combined. Gently fold in the cooled caramelized apples.

Spread the thick batter evenly into the prepared pan. Bake for 28 to 32 minutes until edges are golden and set, the top is crinkly, and a toothpick inserted into the center comes out with moist crumbs (not wet batter).

Allow blondies to cool completely in the pan for at least 1 hour for clean, chewy slices. Lift using parchment handles, drizzle with warm salted caramel, slice into 16 squares, and enjoy!