Preheat oven to 350ºF/ 177℃.
Spray your mini donut pan with cooking spray.
In a standing mixer bowl or a large bowl, whisk together the dry ingredients in a large bowl - flour through sugar.
Whisk the melted and cooled butter, vanilla, egg yolks, and milk in a medium bowl. Make a well in the center of the dry ingredients and pour in. Stir until just incorporated.
Whisk the egg white in a separate small bowl for about a minute or two with a fork. You are just trying to get the egg white to thicken to add fluffiness to the donuts.
Add egg whites to the batter and stir just until incorporated.
Transfer the mixture to a piping bag or Ziploc bag and cut the corner tip off. This makes it easy to pipe the batter into the donut pan.
Fill each mold to the top without covering the middle post.
Bake for about 20 minutes. You should see that the baked donut covers the middle post entirely on the bottom.
Allow to cool completely before removing the mini donuts from the pan and then glazing. When you remove the donuts from the pan, you will see a well or hole in the middle.
Mix the powdered sugar with the desired amount of milk and elderflower cordial for the glaze. Only add a little at one time.
Dip donuts in glaze and place on a wire rack to dry. We recommend placing the wire rack on top of a baking sheet lined with parchment paper.
Serve and enjoy!