Preheat your oven to 350°F (175°C) and grease a mini muffin pan or use silicone molds.
In a large mixing bowl, whisk together the flour, granulated sugar, cocoa powder, baking powder, and salt until well combined.
In another bowl, mix the milk, vegetable oil, eggs, and vanilla extract until smooth.
Pour the wet ingredients into the dry ingredients and stir until just combined. If using, fold in the chocolate chips.
Fill each muffin cup about 2/3 full with the batter.
Bake in the preheated oven for 10-12 minutes or until a toothpick inserted into the center comes out clean.
Allow the donut holes to cool in the pan for 5 minutes before transferring them to a wire rack.
Once cooled, roll each donut hole in powdered sugar until fully coated.