Preheat the oven to 350°F and lightly grease donut pans with cooking spray. This recipe makes roughly 16 mini donuts.
Add oil, white sugar, and brown sugar to a mixing bowl and whisk together until combined. Mix in the egg and vanilla extract, then whisk in the milk.
Add flour, cocoa powder, salt, baking powder, and baking soda to the bowl and mix until combined. Do not over mix.
Fill the donut cavities ½ way full with batter. I recommend squeezing the batter out of a ziploc bag to make it easier. To do this, add the batter into the ziploc bag, then cut the corner off of the bag and pipe the batter into it.
Bake for 7-10 minutes, or until the donuts spring back when you gently press your finger into them. Let cool in the pan for a few minutes then transfer to a wire rack to cool completely. Place a large baking sheet under the wire rack (or a piece of parchment paper), to avoid making a mess once the donuts are glazed.
Chocolate Glaze
Add butter, chocolate chips, and milk to a small pan over low-medium heat, stirring until melted and combined. Remove the pan from the heat and whisk in the powdered sugar.
Transfer the icing to a medium bowl, then dip the donuts upside down in the icing, covering the top. Transfer the donuts back to the wire rack to let the glaze set.
Notes
OIL VS BUTTER: When testing this recipe, I found that when made with oil, the donuts stayed light and fluffy for longer, whereas they dried out a bit quicker with butter. MEASURING FLOUR and COCOA POWDER: Properly measure your flour and cocoa powder using the scoop and level method or a kitchen scale.PAN SIZES: If you don't have a donut pan, you can use a mini muffin pan. These can also be made as regular sized donuts!Storage Instructions: If you've ever bought a box of donuts and tried to eat them the next day, you'll know they, by nature, don't last very long. They are best enjoyed the day they're baked but you can store them for up to 2 days in an airtight container at room temperature if needed. Note that the glaze may start to melt depending on the climate where you live.