Preheat your oven to 350°F (175°C) and prepare a 9x13 inch baking pan by greasing and flouring it or lining it with parchment paper.

In a large mixing bowl, whisk together all-purpose flour, baking powder, baking soda, salt, and ground nutmeg.

In another bowl, combine melted butter, granulated sugar, eggs, buttermilk, and vanilla extract. Whisk until smooth.

Carefully pour the wet mixture into the dry ingredients and gently mix until just combined.

Pour the batter into the prepared baking pan and spread evenly.

Bake for 20 to 25 minutes or until a skewer inserted in the center comes out clean.

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

To prepare the glaze, sift powdered sugar and mix with maple syrup, milk, melted butter, and a pinch of salt until smooth.

Once the bars are cool, pour the glaze over them and add any desired toppings.

Let the glaze set for 30 minutes to 1 hour before slicing into bars.