Preheat the oven to 350°F. Brush melted butter generously all over the cavities of the donut pan and set aside.

In a medium mixing bowl, add the egg, apple butter, oil and vanilla extract, beat to combine. Add the brown sugar to the liquid mixture and whisk to combine.

In a small mixing bowl, sift together flour, baking powder and baking soda. Stir in the kosher salt. Add the flour mixture to the wet ingredients and fold until just combined.

Spoon about 3 ½ tablespoon of batter into each cavity of the prepared donut pan; try to distribute the batter evenly in the ring shape cavity.

Bake for 10 minutes until a toothpick inserted in the middle of donuts comes out clean.

Remove from the oven and allow the donuts to cool for 5 - 10 minutes in the pan before flipping the pan over a wire rack to remove the donuts from the pan and let them cool completely.

If you only have one donut pan, clean it out, butter it again and bake the rest of the batter.

To make the glaze, whisk the maple syrup and powder sugar together in a small bowl until a thick glaze forms.

When the donuts are cool enough, dip one side of the donuts into the glaze, let excess drip back into the bowl. Place the donuts back on the wire rack, set the wire rack on a baking pan to catch any drips. Allow them to rest until the glaze hardens.