Preheat oven to 425°F. Lightly grease donut pans and set aside.
In a large bowl, cream the butter, vanilla and both sugars. Add the egg, sour cream and buttermilk. Mix until well combined.
In a separate medium bowl, combine the baking powder, baking soda, cocoa powder and flour. Gradually add to the wet ingredients. Stir in the chocolate chips.
Fill the donut pan cavities three-quarters of the way full. Bake for 9 minutes. Allow the donuts to cool in the pan for 2-3 minutes before removing to wire racks to cool completely.
After the donuts have cooled, melt the shortening with the chocolate chips in a microwave safe bowl in 30 second increments, stirring after each increment, until the chips are melted and smooth. Dip the donuts in the melted chocolate and decorate with sprinkles, if desired.
Notes
Keep them in a covered container on the counter away from heat and sunlight for up to 3-4 days. For longer storage, put them in the refrigerator for up to 7 days.