Preheat the oven to 400℉. Prepare the 12-count donut pan by spraying generously with cooking spray. I recommend placing the silicon donut pan on a baking sheet for stability.
In a medium bowl, whisk together the dry ingredients: flour, sugar, baking powder, and salt. In a separate bowl, stir together the wet ingredients: milk, melted butter, and vanilla.
Stir the wet ingredients into the flour mixture and mix until just combined to make the doughnut batter. Fold in the blueberry pieces.
Spoon the batter into the greased donut pan. I've found that about three normal sized spoonfuls in each donut pan perfectly fills them up. An alternative way to fill the pans is by pouring the batter into a plastic bag, pastry bag or piping bag and cutting a corner off to pipe it into the molds.
Reduce the oven temperature to 350℉. Bake in the preheated oven for 20 minutes (give or take two minutes). The donuts are done when they spring back when touched and will pull away from the edge of the pan slightly.
Leave the donuts in the pan until they have cooled so that they can be touched without burning fingers. Then invert the pan onto a cooling rack that is setting in a baking sheet. I also like to slip a piece of parchment paper under the cooling rack to catch the extra donut glaze that drips of the blueberry cake doughnuts. This will keep your countertop from getting messy!
Make the frosting by whisking the milk, maple syrup, melted butter, freeze dried blueberry powder and powdered sugar together until smooth. Start with the least amount of milk and then gradually add more, a little at a time, until the desired consistency is reached.
Dip the baked doughnuts upside down into the glaze. Add sprinkles, if desired!