Preheat the oven to 350°F (175°C) and grease a baking pan.

In a mixing bowl, whisk together the flour, sugar, baking powder, and salt.

In another bowl, combine the beaten egg, milk, melted butter, and vanilla extract.

Pour the wet ingredients into the dry ingredients and mix until just combined.

Spread the batter evenly in the prepared baking pan.

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

Allow to cool in the pan for 10 minutes, then transfer to a cooling rack.

In a small bowl, whisk together the powdered sugar, maple syrup, milk, and vanilla extract.

Adjust the milk to achieve desired glaze consistency.

Once the donut bars are completely cool, drizzle the glaze over the top.

Let the glaze set for a few minutes before slicing into bars.