Preheat your oven to 350°F (175°C) and prepare a baking pan by lining it with parchment paper.

In a medium bowl, whisk together the all-purpose flour, baking soda, baking powder, salt, and ground nutmeg until well mixed.

In a large bowl, beat the softened unsalted butter and granulated sugar together until light and fluffy, about 3-4 minutes.

Add the egg, vanilla extract, and buttermilk to the creamed mixture and mix until well combined.

Gradually fold the dry ingredients into the wet ingredients using a spatula, being careful not to overmix.

Pour the batter into the prepared pan and bake for 18-20 minutes, or until a toothpick comes out clean.

Let the bars cool in the pan for about 10 minutes, then transfer to a wire rack to cool completely.

In a medium bowl, whisk together the powdered sugar, maple syrup, maple extract, and milk until smooth.

Once cooled, generously spread or drizzle the glaze over the bars and allow to set before cutting.