Preheat your oven to 350°F (175°C) and grease your donut pan.
In a large mixing bowl, whisk together the dry ingredients: gluten-free flour, cocoa powder, sugar, baking powder, baking soda, and salt.
In another bowl, mix the wet ingredients: milk, vegetable oil, eggs, and vanilla extract until smooth.
Pour the wet ingredients into the dry ingredients and stir until just combined. Fold in chocolate chips if using.
Fill each cavity of the donut pan about 2/3 full with the batter.
Bake for 10-12 minutes, checking for doneness with a toothpick.
Let the donuts cool for about 5 minutes in the pan before transferring to a wire rack.
Optional: Melt additional chocolate chips and drizzle over cooled donuts for a glaze.