Preheat Oven: Set your oven to 350°F (175°C) and greased your donut pan, ensuring that the cavities are well-covered to prevent sticking.

Combine Dry Ingredients: In a mixing bowl, whisk together the all-purpose flour, cocoa powder, light brown sugar, baking powder, baking soda, nutmeg (if you're using it), and salt until thoroughly blended.

Mix Wet Ingredients: In a separate bowl, whisk the buttermilk, egg, melted butter, and vanilla extract together until smooth.

Combine Mixtures: Fold the wet ingredients into the dry mixture, stirring gently until just combined.

Fill Pan: Spoon or pipe the batter into the prepared donut pan, filling each cavity about ¾ full. Bake in the preheated oven for 11-13 minutes until springy to the touch.

Cool: Once baked, let the doughnuts cool in the pan for about 5 minutes before transferring them to a wire rack to cool completely.

Prepare Glaze: While the doughnuts cool, whisk together the confectioners' sugar, milk, vanilla extract, and a pinch of salt until smooth.

Glaze Donuts: Once the doughnuts have cooled, dip the tops into the glaze, allowing any excess to drip off before placing them back on the rack to dry.