For the Donuts:

1. Preheat the oven to 350°F. Butter or spray your donut pan with nonstick cooking spray.
2. Whisk the flour, baking powder, baking soda, cinnamon, nutmeg, and salt together in a medium bowl. Set aside.
3. Whisk the egg, brown sugar, maple syrup, milk, yogurt, melted butter, and vanilla together until smooth and well combined.
4. Pour the wet ingredients into the flour mixture and stir gently until just combined, trying not to overmix the batter.
5. Spoon the batter into a large resealable plastic bag and snip one corner of the bag. Carefully pipe the batter out of the bag into your donut pan, filling each donut well ¾ of the way full.
6. Bake for 8-10 minutes, or until the batter is set and the edges are lightly browned. Cool for a couple minutes in the pan and then carefully transfer the donuts to a wire rack to finish cooling.

For the Salted Maple Glaze:

1. Place the maple syrup in a small pot over medium heat. Bring to a simmer and cook until it is reduced by roughly half.
2. Whisk in the butter until it is completely smooth and melted.
3. Remove the pot from the heat and whisk in the powdered sugar, a little at a time, mixing until a smooth glaze forms.
4. Whisk in ½ teaspoon of the sea salt, taste (carefully! It will be warm), and add more sea salt if needed.
5. If the glaze gets too thick as it cools, whisk in 1-2 teaspoons of water until it becomes a drizzling consistency.

To Glaze:

1. Dip each donut in the warm glaze and return them to the cooling rack to sit until the glaze has set, about 10 minutes. If desired, sprinkle each donut with a little extra flaky sea salt before the glaze has completely hardened.