Donut Bars:

1. Preheat oven to 350°F (175°C). Grease and flour a 9×13 inch baking pan.
2. In a large bowl, cream together the butter and sugar until light and fluffy.
3. Beat in the eggs one at a time, then stir in the vanilla extract.
4. In a separate bowl, whisk together the flour, baking powder, baking soda, nutmeg, and salt.
5. Gradually add the dry ingredients to the wet ingredients, alternating with the buttermilk, beginning and ending with the dry ingredients. Mix until just combined. Do not overmix.
6. Pour batter into the prepared pan and spread evenly.
7. Bake for 20-25 minutes, or until a wooden skewer inserted into the center comes out clean.
8. Let cool in the pan for 10 minutes before transferring to a wire rack to cool completely.

Brown Butter Maple Vanilla Bean Glaze:

1. In a small saucepan, melt the butter over medium heat. Continue to cook, swirling occasionally, until the butter is golden brown and has a nutty aroma (about 5-7 minutes). Remove from heat and let cool slightly.
2. In a medium bowl, whisk together the powdered sugar, maple syrup, vanilla extract, and vanilla bean seeds.
3. Gradually whisk in the browned butter until smooth.
4. Add milk, 1 tablespoon at a time, until the glaze reaches your desired consistency.
5. Once the donut bars are completely cool, drizzle the glaze over the top. Let the glaze set before cutting into bars and serving.