Preheat to 350°F, then spray your donut pan with non-stick cooking spray and set aside.
Whisk together your dry ingredients (flour, brown sugar, salt, baking powder) in a large bowl and set aside.
In a separate bowl, mix together the butter, egg, sour cream, maple syrup, and vanilla until well combined. Gently fold the wet ingredients into your dry ingredients until just combined (note: dough will be very thick).
Place your dough into a piping bag (or gallon sized ziplock bag) to pipe into your donut pans. If desired, gently smooth out the tops after all of the dough has been distributed into your donut pan.*
Bake approximately 12-15 minutes, until a toothpick comes out clean.
Cool in the pan for a few minutes, then turn out onto a cooling rack to cool completely.
While the donuts finish cooling, make your maple glaze in a small bowl by mixing together all glaze ingredients until smooth.*
When the donuts have cooled, dip the top half of each donut into the glaze and set up-right on your cooling rack to set.*
Baked donuts are best day-of, but if any remain, store in an air-tight container in the fridge for a day or two.