Preheat oven to 350 degrees. Spray you doughnut pans with nonstick spray and set aside. Add flour, baking powder, and salt together in a large bowl. Whisk together until combined. Set aside
In the bowl of stand mixer, place butter and sugar and beat together until smooth. Add vanilla and 1 egg. Beat until smooth. Add other egg and beat until smooth. Add smashed blueberries and buttermilk to batter and mix just until combined. Add all of the flour mixture to batter and mix just until combined. Do not over mix!
Place batter into a plastic storage bag to make filling the doughnut mold easy. If you do want to use a storage bag, you can simply spoon it in, but that will take longer. Snip the corner of the bag and fill doughnuts molds completely. I had 12 molds so I needed to wait until the 12 cooked before making the other 6.
Sprinkle crumbs (from recipe above) over the filled doughnut molds. Cover the batter completely with crumbs. Bake for 15 minutes, or until doughnuts begin to brown very slightly around the edges. Remove from oven and let cool for 10 minutes in the pan. Then, remove from pan and cool completely on cooling rack.
If you want to sprinkle with powdered sugar, wait until completely cooled or else the doughnut will absorb the powdered sugar. If presentation is not a concern, go ahead and sprinkle when warm and eat immediately.
Store doughnuts in a storage container lightly sealed with foil so that the moisture isn't trapped. Doughnuts are best on the same day but will stay good for the next day or so.