• Adjust oven rack to middle position and heat to 400°. Spray donut pan with vegetable oil spray. Whisk flour, sugar, chocolate chips, cocoa powder, cornstarch, baking powder and salt together in a bowl.
• Whisk buttermilk, butter, eggs, and yolk in a second bowl.
• Add the wet ingredients into the dry ingredients and stir until just combined.
• Pipe batter into prepared donut pan. Fill about ¾ full. This should give you about 9 donuts.
• Bake until toothpick inserted in center comes out clean. 8 to 10 minutes. Let donuts cool in pan for 5 minutes.

For the Glaze:

• Combine chocolate chips, butter, corn syrup and vanilla in a double boiler until melted.
• Dunk your donuts into the glaze making a swirling motion as you pull it out.
• We then sprinkled chopped up chocolate chips onto the top.