Grease the donut pans well (I use butter). Set them aside.
In a large mixing bowl, sift the flour, cocoa powder, baking powder, and baking soda together.
1 ½ cups (188g) all purpose flour, ½ cup (60g) unsweetened cocoa powder (I use Dutch-processed), 1 teaspoon baking powder, ½ teaspoon baking soda
Add the sugar and the salt and whick together to combine.
¾ cup (150g) light brown sugar, ¼ teaspoon salt
In another medium-sized bowl, whisk together the eggs, milk, vinegar and melted butter.
2 medium eggs, at room temperature, 1 cup (250ml) milk, at room temperature, 1 tablespoon white vinegar, 2 tablespoons (30g) unsalted butter, melted (+ extra to grease the pan)
Pour the wet ingredients into the dry ingredients and whisk together until well-combined. Don't overmix it.
Put the batter into a jug and pour it in the the donut cavities, about ¾ full.
Bake the donuts for 12-13 minutes, or until a toothpick inserted in one comes out clean. Don't overbake them, or they'll get dry.
Let the donuts in the pans for about 10 minutes before removing them. Transfer them to a wire rack to cool completely.
Make the ganache topping
Place the milk and chocolate chips in a microwave-safe bowl. Heat on high power in 10-second increments, stirring well after each interval. Tip:Keep an eye on the mixture to avoid burning! Once the chocolate chips are mostly melted with a few lumps remaining, stop heating and continue stirring until completely smooth.
1 cup (170g) chocolate chips (or 6oz semisweet chocolate, finely chopped), ¼ cup milk (60ml)
Carefully dip the tops of each donut in the thick chocolate ganache or use the back of a spoon to spread it on the donuts.
Garnish with chocolate sprinkles (if using) while the ganache is still wet, so that they stick.