Preheat your oven to 350°F (175°C).
Lightly grease your donut pan with cooking spray or oil.
In a large mixing bowl, whisk together the flour, brown sugar, salt, baking powder, and cinnamon.
In another bowl, whisk together the milk, melted butter, and egg until smooth.
Pour the wet ingredients into the dry ingredients. Fold gently until just combined.
Spoon the batter into the prepared donut pan, filling each cavity about 2/3 full.
Bake for about 10-12 minutes, or until golden brown.
Let cool for a few minutes before transferring to a cooling rack.
In a small bowl, whisk together the confectioners' sugar, granulated sugar, milk, and cinnamon until smooth.
Dip the tops of each donut into the glaze, allowing excess to drip off.