This recipe makes a little over a quart of ice cream. My ice cream maker is the Cuisinart Ice-40, amounts and process will need to be adjusted for other makers.
Put the cream and milk into a large saucepan. If using a vanilla bean pod, slice it lengthwise, and using the back of the knife scrape the seeds into the pan. Then put the pod in the pan. Bring to a simmer, and simmer for 30 minutes, stirring regularly. Take off heat, and remove the pod and discard.
Beat the yolks, sugar, and cocoa powder into a paste. Slowly add about a cup of the warm milk/cream into the paste, while beating. Melt the chocolate chips into the rest of the milk/cream, in the saucepan. Put the saucepan back on the burner, on medium-high, and stir in the yolk mix.
Bring to a boil, then reduce to a simmer, and keep at a simmer for several minutes, stirring constantly. It should thicken slightly. Remove from the heat and stir in the vanilla extract, if you didn't use a vanilla bean pod.
Allow to cool. Pour evenly into two containers, cover, and put in fridge. After it has finished cooling, it should continue sitting in the fridge for at least 6 hours but no more than 3 days.
The ice cream barrels should be in the freezer for 24 hours before starting. Take them out of the freezer, and set up and start the ice cream maker. Add one container of base to each barrel, and start the timer.
After 25 minutes, the ice cream should be ready. Put into one or more containers, and put in freezer. Allow to harden in freezer for at least four hours.
Don't freeze the barrels with ice cream in them. Allow them to thaw and then clean and dry them thoroughly before putting them back in the freezer. Enclose them in plastic bags in the freezer, to prevent frost.
I usually use 40% heavy cream that I get from Costco, but any heavy cream will work. I use either 2% or 1% milk, depending on what I have in the fridge. I use Costco's 51% chocolate chips for the chocolate. When I have it, I use Valrhona cocoa powder, otherwise I just use whatever other cocoa powder I happen to have.
While simmering the milk/cream mixture, I usually make meringue cookies from the extra egg whites. If one of the yolks break, I just toss that white in with the yolks.