In a heavy saucepan over medium heat, add heavy cream and milk. Bring to a simmer. Remove from heat. Stir in mint leaves (NOT the minced ones). Cover with a lid and steep for 2 hours.
In another heavy saucepan, whisk together egg yolks and sugar until thicken and pale in color. Strain the cream mixture through a sieve into the egg yolks. Whisk for a minute. Use the back of a spoon to press out as much extract as possible from the mint leaves. Whisk to combine.
Set the saucepan over medium heat. Cook until the mixture is thickened enough to coat the back of the spoon or reaches 170˚F (76˚C). Remove from heat. Stir in salt.
Let the mixture cool at room temperature for 1 hour. Pour the mixture through a fine-meshed sieve into an air-tight container. Cover and refrigerate until completely chilled, about 5 hours or overnight.
When the ice cream mixture is ready to be churned, whisk in the minced fresh mint. Pour the mixture into an ice-cream maker by following the ice-cream maker instruction.
While the ice cream is churning, place the chopped chocolate and the vegetable oil in a small microwave-safe bowl. Mix with a spoon. Microwave for 15 seconds. Stir and microwave for another 15 seconds. Repeat the process until the chocolate is just melted and smooth. Set aside.
At the last 3 minutes of the churning, slowly drizzling in chocolate into the ice cream. For better result, drizzle a tablespoon or so. Let the machine run for a few times. Add another tablespoon of chocolate. Repeat until there is no more chocolate or to your taste.
Transfer the ice-cream to a container and freeze for at least 4 hours before serving.