How to Make It
Combine the mint, milk, sugar, cream, and salt in a large saucepan. Bring to a simmer over medium heat and cook, stirring occasionally, until the sugar is dissolved, 3 to 5 minutes. Remove from heat and let steep for 30 minutes.
Strain the milk mixture through a fine-mesh sieve into a large bowl, pressing to extract as much of the liquid as possible; discard the mint. Return the milk mixture to the saucepan and place over medium-low heat.
Set the sieve over a medium bowl. In a separate bowl, whisk the egg yolks. Slowly add 1 cup of the warm milk mixture to the egg yolks, whisking constantly, until combined. Return to the saucepan with the remaining milk mixture and cook, stirring constantly, until the mixture thickens to a custard and coats the back of a spoon, 10 to 12 minutes.
Remove the custard from heat and strain. Let sit until slightly cool, about 10 minutes. Refrigerate, covered, until cold, at least 3 hours and up to overnight.
Transfer the custard to an ice cream maker and freeze according to the manufacturer’s instructions. Fold in the chocolate. Transfer the ice cream to an airtight container and freeze until firm, at least 4 hours and up to 4 days.