1) Preheat your oven to 350°F and lightly grease two doughnut pans.
2) Mix the flour, cornstarch, baking powder, baking soda, salt, and xanthan gum in a bowl, and set aside.
3) With an electric mixer and paddle attachment, beat the butter and maple sugar until they're fluffy and the sugar begins to dissolve, about 2 minutes. Then add the eggs, one at a time, beating well.
4) Stir the maple flavoring into the milk and add it alternately with the blended dry mixture to the butter/sugar.
5) Beat the batter on medium speed for approximately 30 seconds, then scrape the sides of the bowl and beat for an additional 30 seconds.
6) Fill a large piping bag (or zip-top bag) with the batter, and pipe it into your prepared doughnut pans. Allow the batter to rest for 10-15 minutes before baking.
7) Bake the doughnuts for 15 minutes. Remove them from the oven, and allow them to rest for just a minute or two before turning them out onto a rack to cool.
8) To make the glaze: Mix all of the glaze ingredients, stirring until smooth.
9) Dip the cooled doughnuts into the glaze and turn them out onto a cooling rack set atop parchment paper, to catch the drips.
Yield: 12 doughnuts.