01 - Preheat oven to 350°F and line a 9x13-inch baking pan with parchment paper, leaving an overhang for easy removal.
02 - In a large bowl, cream butter and brown sugar together until light and fluffy.
03 - Beat in eggs one at a time, then mix in maple syrup and vanilla extract until incorporated.
04 - In a separate bowl, whisk flour, baking powder, baking soda, salt, cinnamon, and nutmeg.
05 - Gradually add dry ingredients to wet mixture, stirring just until combined.
06 - Evenly spread batter into the prepared pan.
07 - Bake bars for 22 to 25 minutes, or until a toothpick inserted in the center comes out clean. Avoid overbaking.
08 - Allow bars to cool completely in the pan placed on a wire rack.
09 - In a small bowl, whisk powdered sugar, maple syrup, 1 tablespoon milk or cream, and salt until smooth. Add more milk if needed to achieve a pourable consistency.
10 - Drizzle or spread glaze evenly over cooled bars and let set before slicing into squares.