01 - Preheat the oven to 375°F (190°C) and grease two standard donut pans.
02 - In a large bowl, whisk together flour, cocoa powder, sugar, baking powder, baking soda, and salt until evenly mixed.
03 - In a separate bowl, whisk whole milk, eggs, vanilla extract, melted butter, and vegetable oil until smooth.
04 - Add the wet mixture to the dry ingredients and stir gently until just combined, avoiding overmixing to preserve fluffiness.
05 - Transfer batter into a piping bag or zip-top bag, snip off the tip, and pipe batter into greased pans, filling each cavity approximately two-thirds full.
06 - Bake for 13 to 15 minutes or until a toothpick inserted into a donut comes out clean. Let cool in the pans for 5 minutes before transferring to a wire rack to cool completely.
07 - Whisk powdered sugar, cocoa powder, milk, and vanilla extract until smooth and glossy. Adjust milk quantity to achieve desired consistency.
08 - Dip the cooled donuts' tops into the glaze and place them back on the wire rack to set for at least 10 minutes before serving.