Preheat the oven to 350 °F (176 °C) and line an 8"x8" pan with a sheet of parchment paper.
In a medium mixing bowl, stir together the flour, 1 tablespoon cinnamon (ignore the quantity below - it's a technical issue I can't fix), nutmeg, baking powder, baking soda and salt. Set aside.
1 1/2 cups (188 grams) flour, 1 tablespoon + 1/2 teaspoon ground cinnamon, 1/8 teaspoon ground nutmeg, 1/2 teaspoon baking powder, 1/8 teaspoon baking soda, 1/2 teaspoon salt
In a large mixing bowl, stir together the melted butter, brown sugar, and vanilla extract.
1/2 cup (113 grams) unsalted butter, 1 1/2 cups (300 grams) light brown sugar, 1 teaspoon vanilla extract
Beat in the eggs, one by one, and stir just until combined.
2 large eggs
Fold in the dry mixture, stirring just until no streaks of flour remain.
Mix the peeled apple chunks with the remaining 1/2 teaspoon of cinnamon (ignore the quantity below - it's a technical issue I can't fix) and fold the cinnamon apples into the batter, making sure not to overmix.
1 1/2 cups (180 grams) Granny Smith apple peeled chunks, 1 tablespoon + 1/2 teaspoon ground cinnamon
Pour the batter into the prepared pan and bake for 25-32 minutes or until the edges have lightly browned and the middle jiggles just slightly.
Place the pecans on a rimmed cookie sheet and bake them for 4-7 minutes, stirring them halfway through, or until they smell roasted. Remove from the oven and let cool completely.
1 cup (110 grams) chopped pecans
When the blondies have cooled, prepare the frosting.
In a small saucepan over medium heat, mix together the brown sugar, butter, milk and salt.
6 tablespoons (75 grams) light brown sugar, 3 tablespoons (42 grams) unsalted butter, 2 tablespoons + 3/4 teaspoons milk, pinch salt
Whisking continuously, bring the mixture to a boil and boil for 1 minute, while continuing to whisk continuously. Remove the pan from the heat and stir in the salt and vanilla (it will bubble).
3/4 teaspoon vanilla extract
Gradually whisk in 2/3 cup powdered sugar and mix until smooth and no lumps of sugar remain. Taste and add up to another 1/3 cup powdered sugar, if desired.
2/3 - 1 cup (80 to 120 grams) powdered sugar
Stir occasionally for about 3 minutes or until the frosting has slightly thickened. Immediately pour over the cooled blondies. If it's thickened too much, place back on the heat for a few moments.
Spread the frosting over the cooled blondies and top with the chopped pecans.
Refrigerate in an airtight container for up to 4 days. Can be stored at room temperature for 1 day.