Based on the recipe found here.
BEST DARK CHOCOLATE FROZEN CUSTARD
4 oz. semisweet chocolate, coarsely chopped (can use chips)
1/3 c. unsweetened cocoa powder (Barry or Perugina)
1 c. sugar, divided
2 c. whole milk
2-1/3 c. heavy whipping cream
2 large eggs, plus 4 large egg yolks
1 tsp. vanilla
Place chocolate pieces into a deep, heatproof bowl and set aside.
Place cocoa powder and 1/2 c. sugar in a large saucepan and combine with a whisk. Slowly pour in the milk, while continuing to whisk, then add the cream. Turn the burner on medium high heat and bring to a boil while stirring continuously. Boil for 2 minutes. Remove from heat and set aside. Whisk occasionally to keep a skin from forming.
In a medium non-aluminum bowl, whisk the remaining 1/2 c. sugar, eggs and egg yolks until mixture is light yellow. Temper the egg mixture by slowly adding a cup of the cocoa mixture to it.
Pour 1/3 cup of the cocoa mixture over the chocolate in the bowl set aside earlier. Stir to melt the chocolate. Add another 1/3 c. of the cocoa mixture and stir until smooth.
Add the egg mixture into the saucepan with the remaining egg mixture. Place over medium low heat. Continue stirring and heat until mixture thickens and coats the back of a spoon (around 160 degrees).
Remove from heat and stir for 30 more seconds. Stir a cup of the hot mixture into melted chocolate. Stir until smooth. add chocolate mixture and vanilla into the egg mixture and stir until well incorporated.
Pour through fine sieve. Cover a refrigerate for at least 6 hours. Process in ice cream maker according to manufacturer directions.