Preheat oven to 350 degrees F. Prepare doughnut pans with cooking spray.
In a large mixing bowl, mix together the flour, baking powder, salt, and cinnamon; set aside.
In a medium bowl, mix together butter and sugar, and beat together until combined. Add egg whites and oil to the medium bowl, and mix until combined.
Add the flour mixture, and mix until combined. It will be a little dry, since you haven’t added the milk.
Finally, add the milk and mix completely.
Divide the batter evenly among the prepared pans.
Bake for 10-12 minutes, or until lightly brown around the edges and a toothpick inserted in the center of the cakes comes out clean. Cool the doughnuts in the pans on a wire rack for 10 minutes.
Meanwhile, prepare the simple glaze by mixing together the ingredients in a small bowl. Slowly add the milk until the desired consistency is reached.
Whlie still warm, carefully remove the doughnuts from the pans, place them on a wire rack, and pour over your desired amount of glaze.
Enjoy!