Preheat the oven to 350°F (175°C) and lightly grease a donut pan; set aside.
In a large bowl whisk together the flour (including the extra 2 tablespoons), dark brown sugar, salt, and baking powder until evenly combined.
In a separate bowl whisk together the milk, melted butter, egg, and vanilla extract until smooth.
Gently fold the wet ingredients into the dry ingredients and stir until just combined; avoid overmixing—the batter should be thick.
Spoon or pipe the batter into the prepared donut pan, filling each mold about three-quarters full.
Bake for 10–11 minutes, until the donuts spring back when lightly pressed. Let them cool in the pan a few minutes, then transfer to a wire rack to cool further.
Place the chocolate chips in a wide, heatproof bowl. Heat the heavy cream in a small saucepan over medium heat until it comes to a boil, then immediately remove from heat.
Pour the hot cream over the chocolate chips and let sit for 1 minute, then whisk until smooth to make a ganache. Allow the ganache to cool slightly before dipping.
Dip each cooled donut into the ganache, letting excess drip back into the bowl, then return to the rack. Decorate with sprinkles while the ganache is wet if desired.
Let the ganache set for a few minutes then serve.