Preheat oven to 350 F. Grease donut pan well with butter or cooking spray and set aside.

In a large bowl, mix the dry ingredients together (flour, sugar, salt, and baking powder). Set aside.

In a small bowl, whisk buttermilk, butter, and egg together. Stir wet ingredients into dry ingredients and mix until just combined. Fold blueberries into batter gently.

Place batter in large plastic bag with end cut off about ?". Fill donut cavities about ?" full and slam pan on floor or countertop to get dough to settle.

Bake for 20-22 minutes until tops are lightly browned and when you push on donut it springs back.

Let donuts cool in pan for 10 minutes before gently inverting pan and taking donuts out.

While donuts are cooling, whisk glaze ingredients together. When donuts are cooled completely, dip tops of donut into glaze.