• Make the doughnuts. While the doughnuts are doing their last proof, make the cream filling.

Filling

• Make the filling: In a small bowl whisk the egg yolks together. 
• In a saucepan over medium heat whisk the sugar, cornstarch, salt, and milk. Stir constantly until the mixture starts to thicken and bubble. Simmer for 2 minutes or until the mixture is thicker, then remove from heat. 
•  Measure out ½ cup of the warm milk mixture. Slowly stream the warm milk into the bowl of egg yolks, whisking constantly while doing so. Add the now tempered eggs into the saucepan full of the milk mixture, whisking constantly as you do so. Bring the mixture to a  boil. Boil for 2 minutes, stirring constantly. The mixture should be quite thick at this point. Remove from heat and stir in the butter and vanilla. Stir until smooth. Strain through a fine mesh sieve into a medium sized bowl.
• Cover with plastic wrap (have the plastic wrap touching the mixture so that a film doesn’t develop) and chill until cool, about 3-4 hours. 
• When ready to fill doughnuts, remove the mixture from fridge and give it a stir. Place in a pastry bag. 

Chocolate Glaze

• Make the chocolate glaze: In a small bowl sift the powdered sugar and cocoa together.
• Place the chocolate chips and butter in a medium sized bowl.
• Heat the cream in a small pot over medium heat until bubbling along the perimeter. Pour the hot cream over the chocolate and butter. Let stand for 1 minute. Stir until chocolate has melted. Whisk in the powdered sugar + cocoa mixture, and vanilla. The mixture should have the consistency of hot fudge sauce. If too thick add more heavy cream 1 tablespoon at a time. 
• Fill a large saucepan or pot over medium heat. Oil should be heated between 360°F-375°F. Fry doughnuts until golden in color.
• When done frying tranfer the doughnuts to a papertowel lined plate or baking sheet. Using a chopstick, insert the stick in the side of one doughnut. This helps create a hole for you to insert the tip of the cream filled pastry bag. Fill the doughnuts with 1-2 tablespoons of the cream filling.
• Dip the filled doughnuts in the chocolate glaze until halfway submerged, evenly coating one side. Place the newly glazed and filled doughnuts, glaze-side up on a wire rack. Let stand until the glaze sets. Best when enjoyed the same day they're made.