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.