01 - Preheat oven to 350°F. Lightly grease a donut pan with oil or nonstick cooking spray.
02 - In a medium bowl, whisk together the flour, baking powder, baking soda, salt, and cinnamon until well blended.
03 - In a large bowl, beat the sugar, eggs, Greek yogurt, oil, and vanilla extract until smooth and fully combined.
04 - Gradually add the dry ingredients to the wet ingredients, mixing gently until just incorporated. Avoid overmixing to keep the donuts tender.
05 - Transfer the batter to a piping bag or zip-top bag with one corner snipped off. Pipe the batter evenly into the prepared donut pan, filling each cavity about 2/3 full.
06 - Bake for 10-12 minutes until the donuts are lightly golden and a toothpick inserted into the center comes out clean.
07 - Let the donuts cool in the pan for 5 minutes, then carefully remove them and transfer to a wire rack to cool completely.
08 - Whisk together the powdered sugar, milk, and vanilla extract until smooth. Dip the cooled donuts into the glaze and place them back on the rack to set.