In a medium pot, bring milk and cream to a boil. Remove from heat and add chopped mint. Cover pot and let steep for 20 minutes.
Strain mixture and discard mint leaves. Place pot over medium heat bring back to a boil.
Meanwhile, place 8 oz chopped chocolate in a large bowl. Set aside. In another large bowl, whisk together yolks and sugar.
Once milk begins to boil, lower heat. Temper hot milk into sugar yolk mixture. Slowly add hot milk into yolks about ¼ cup at a time, whisking to distribute heat. Once all the milk has been added, transfer everything back into the pot.
Stir over medium-low heat until mixture reaches nappe consistency, or 180°F on a kitchen thermometer. Let sit at 180° F for 3 minutes to pasteurize eggs.
Pour hot mixture into bowl of reserved 8 oz chopped chocolate. Cover with plastic wrap and let sit for 3 minutes. Remove plastic wrap and stir to combine. Continue to stir until chocolate has melted and mixture is smooth and homogenous. Transfer mixture to an airtight container and let mature in the fridge overnight (or least6 hours).
Freeze mixture in ice cream maker according to your unit's instructions. Once the volume has increased by half and mixture has reached a soft serve consistency, add in remaining 4 oz chopped chocolate.
Once chopped chocolate has been distributed, transfer ice cream to an airtight container and let rest in the freezer for at least 30 minutes before serving.