Preheat oven to 325 degrees F. Spray a 6 count doughnut pan with cooking spray.
Stir the flour, cocoa powder, baking soda, salt and brown sugar together in a bowl.
In a second bowl, whisk together buttermilk, egg, vanilla, butter and oil.
Add the flour mixture and stir with a heavy duty scraper until well blended.
Spoon two generous tablespoons of batter into 6 doughnut cavities. You will have enough batter leftover to make 4 more doughnuts.
Bake for 12 minutes or until cakes spring back when touched.
Let cool in pan for 3 minutes, then flip onto a cooling rack.
To make the glaze, put the butter, corn syrup and chips in a microwave safe measuring cup or bowl. Microwave at 50% power, stirring every 30 seconds until smooth. Add hot water to thin, then drizzle over doughnuts. Alternatively, you can put the glaze in a shallow bowl and dip the doughnuts.
To make vanilla glaze, melt the butter in a microwave-safe glass measuring cup. Add sugar and stir until mixed, then stir in milk (as needed) until smooth. Add vanilla. Spoon over doughnuts or transfer to a bowl and dip the doughnuts.
Notes
Adapted from Full Circle Magazine via Shutterbean.Make sure to either weigh the flour or really aerate it well before measuring so that you don't accidentally use too heavy a cup.