1/2cupsour cream (I used full-fat but think reduced fat will work fine)
2 1/2tablespoonsunsalted butter, melted
1large egg, at room temperature
1/4cupfresh blueberries (be sure not too add more or they will become too soft)
For the Cinnamon Sugar Coating:
3tablespoonsunsalted butter, melted
For the glaze:
1cupconfectioners' sugar, sifted
Preheat oven to 350 degrees (F).
Generously grease a doughnut pan; set aside.
In a large bowl whisk together the dry ingredients; set aside. In a separate bowl whisk together the sour cream, butter, and egg.
Gently fold the wet mixture into the dry mixture - careful not to over mix! Quickly fold in blueberries.
Spoon mixture into prepared doughnut pan, and bake for 10-11 minutes, or until the doughnuts spring back when lightly pressed. Allow doughnuts to cool a few minutes in the pan before transferring to a wire wrack to cool completely.
Once the donuts are cooled fully, melt the butter for the cinnamon sugar coating; set aside. Mix the sugar and cinnamon together in a medium-sized bowl; set aside.
For the Glaze: In a small bowl combine the confectioners sugar, milk, and salt; whisk smooth. The glaze should be thick but easily pourable; add more milk/sugar as needed.
Dip the firm, completely cooled donuts in the melted butter, then roll them in the cinnamon sugar mixture; repeat until all donuts have been covered.
Drizzle a swirl of glaze on each donut and serve! These are best eaten the day they are made.