Step 1: Preheat the Oven - Start by preheating your oven to 350°F (175°C).
Step 2: Prepare Your Donut Pan - Grease your donut pan with cooking spray or melted butter.
Step 3: Mix Dry Ingredients - In a medium mixing bowl, whisk together the cake flour, baking powder, and salt.
Step 4: Combine Wet Ingredients - In another bowl, mix the granulated sugar and lemon zest. Then add the buttermilk, egg, melted butter, and vanilla extract. Whisk until smooth.
Step 5: Combine Mixtures - Gradually fold the dry ingredients into the wet mixture using a spatula.
Step 6: Fill the Donut Pan - Fill each donut cavity about ¾ full with the batter.
Step 7: Bake - Bake for about 10-12 minutes until lightly golden.
Step 8: Cool - Let the donuts cool in the pan for about 5 minutes, then transfer to a cooling rack.
Step 9: Serve & Enjoy - Glaze, dust with powdered sugar, or enjoy plain.