Preheat the oven to 350 degrees F. Line a 9x13 inch baking dish with parchment paper.Add the butter to a medium pot set over medium heat. Allow the butter to brown, until it smells toasted, about 2-3 minutes. Stir often. Remove from the heat and stir in the apple butter and 1 cup brown sugar. Let cool 5 minutes. Whisk in the eggs and vanilla. Add the flour, baking powder, 1 teaspoon of the cinnamon, nutmeg, and salt, mixing until just combined. Spread the dough out into the prepared dish. In a bowl, toss the apples with 1/2 cup brown sugar and 1 teaspoon cinnamon. Evenly sprinkle the apples over the dough. Transfer to the oven and bake for 25-30 minutes, just until set in the center. If there is liquid in the center, swirl it around the pan, then bake another 5 minutes. Let cool. Meanwhile, make the glaze. Add the butter to a small pot set over medium heat. Allow the butter to brown lightly until it smells toasted, about 2-3 minutes. Remove from the heat and whisk in the maple syrup, powdered sugar, cinnamon, and a pinch of salt. Drizzle the glaze over the bars. Let set for 5 minutes. Cut into bars...snack and enjoy!