Preheat your oven to 350°F (175°C) and grease a baking pan.
In a mixing bowl, combine flour, baking powder, baking soda, nutmeg, and salt.
In another bowl, cream together softened butter and sugar until light and fluffy.
Add eggs and vanilla extract to the butter mixture, mixing well.
Alternate adding the dry ingredients and buttermilk to the butter mixture, mixing until just combined.
Pour the batter into the prepared baking pan and bake for 15-20 minutes.
While baking, melt butter for the glaze in a saucepan, then add powdered sugar, maple syrup, and vanilla bean paste, mixing until smooth. Add milk to reach desired consistency.
Once the donut bars are cool, drizzle with glaze and serve.
Notes
You can adjust the thickness of the glaze by adding more or less milk.