Preheat Oven and Grease Pans:

Heat oven to 350°F (175°C). Coat donut pans with non-stick spray.

Mix Batter Until Smooth:

In a large bowl, whisk together cake mix, egg, oil, milk, and vanilla extract with an electric mixer or whisk until smooth.

Fill Donut Cavities:

Pour batter into a large piping bag or Ziploc bag. Cut off a corner and fill each donut cavity to 3/4 full.

Bake Until Golden:

Bake for 10-12 minutes until donuts are light golden and a toothpick inserted in center comes out clean.

Cool Donuts on Rack:

Cool in pan for 5-10 minutes, then move to a wire rack to cool fully (about 10-15 minutes).

Prepare Three Glazes:

While donuts cool, make the three glazes. For each glaze, whisk all ingredients in a bowl. Transfer each to a shallow bowl for dipping. Each should be pourable but not runny; thin with extra milk if needed.

Line Baking Sheet:

Line a baking sheet with parchment paper and place it under the wire rack holding the donuts.

Dip Donuts in Glaze:

Dip the top of each donut into the glaze for a few seconds, let excess drip off, then invert and set on the wire rack to firm up.

Add Toppings While Wet:

Optionally, top with sprinkles, chopped candies, or nuts while the glaze is still wet.