Preheat the oven to 350°F (175°C) and line a 9x13 inch baking dish with parchment paper.

In a medium pot, melt the salted butter over medium heat until it turns light brown and releases a nutty aroma.

Stir in apple butter and light brown sugar until smooth, then mix in eggs one at a time, followed by vanilla extract.

In a separate bowl, whisk together flour, baking powder, cinnamon, nutmeg, and salt. Fold dry ingredients into the wet ingredients until just combined.

Dice apples and toss them with remaining brown sugar and a pinch of cinnamon, then fold into the batter.

Spread the batter into the baking dish and bake for 25-30 minutes, checking for doneness with a toothpick.

While cooling, prepare the glaze by browning more butter and mixing it with maple syrup, powdered sugar, cinnamon, and sea salt until smooth.

Drizzle the glaze over cooled blondies and let set for 15 minutes before slicing.