Place the base of an ice cream maker in the freezer for a minimum of 24 hours before churning the ice cream.
In a small saucepan over medium heat, whisk together 1 cup of heavy cream and the cocoa powder. Bring to a simmer and cook for 30 seconds.
Remove the pot from the heat. Whisk in the chocolate until fully melted.
Stir in the remaining 1 cup of heavy cream, then transfer the chocolate cream to a large bowl. Top the bowl with a sieve and set aside.
In a medium saucepan over medium heat, combine the milk, sugar and salt. Whisk until the sugar dissolves and the milk steams, about 10 minutes. Remove the pot from the heat.
In a separate medium bowl, whisk the egg yolks until well combined. Slowly pour the warm milk into the egg yolks while whisking constantly to create a custard.
Transfer the custard back to the saucepan and cook over medium heat, while whisking constantly, until the custard coats the back of a spoon, about 5 minutes.
Immediately pour the custard through the prepared sieve and into the chocolate cream. Add the vanilla extract. Stir until all the ingredients are combined.
Fill a large bowl halfway with ice and cold water. Place the bowl of custard over the ice bath and let cool to room temperature. Once cool, transfer the custard to an airtight container, place plastic wrap directly against the custard, cover and chill in the refrigerator for 1 hour or up to 2 days.
Place the custard in the base of an ice cream maker and churn until the ice cream is thick and smooth, about 10 to 12 minutes.
Transfer the ice cream to a large bowl and stir in the brownie pieces until evenly distributed. Transfer the ice cream to an airtight container and freeze for 4 hours.
The ice cream can be stored in the freezer for up to 30 days.
Recipe adapted from: “The Perfect Scoop” by David Lebovitz