To make the donuts, preheat oven to 350 F. Spray two (6-count) doughnut pans with a flour-based baking spray, like Baker's Joy. Place a wire cooling rack over a rimmed cookie sheet or a piece of parchment paper
In a small bowl, stir water and yeast together. Let the yeast sit for 5-10 minutes, or until foamy.
Meanwhile, in a large bowl, whisk together the flour, sugar, baking powder, cinnamon, and salt.
Make a well in the center of the dry ingredients.
Add the eggs, yogurt, butter, milk, vanilla, and yeast mixture; stir until combined.
Spoon batter into prepared pans, smoothing as needed.
Bake for about 10-15 minutes, or until set and golden brown.
Let the donuts cool in the pan for about 5 minutes.
Meanwhile, prepare the glaze.
In a small bowl, whisk together the powdered sugar, milk, and desired amount of cinnamon.
Remove donuts to wire rack, and drizzle with glaze.
Donuts are best enjoyed warm.
Notes
*If you prefer to use regular (not Greek) yogurt, increase the yogurt to 1 cup and omit the milk.**Nutrition facts are estimates.