01 - Preheat oven to 350°F. Lightly grease a donut pan with oil or nonstick cooking spray.
02 - Whisk together flour, baking powder, baking soda, salt, and cinnamon in a medium bowl until well blended.
03 - Beat sugar, eggs, Greek yogurt, vegetable oil, and vanilla extract in a large bowl until completely smooth and incorporated.
04 - Gradually fold dry ingredients into wet mixture, stirring gently just until combined. Avoid overmixing to maintain tender texture.
05 - Spoon batter into a piping bag or sealable plastic bag with corner snipped. Pipe batter evenly into prepared pan, filling each cavity approximately 2/3 full.
06 - Bake for 10-12 minutes until lightly golden and a toothpick inserted into center comes out clean.
07 - Let donuts rest in pan for 5 minutes before carefully transferring to wire rack to cool completely.
08 - Whisk powdered sugar, milk, and vanilla until smooth. Dip tops of cooled donuts into glaze and place on rack to set.