Make the Custard Base:

1. In a small saucepan set over medium-high heat, heat 1 cup heavy cream with the milk until wisps of steam start to rise from the surface. Immediately remove from heat and stir in the mint leaves. Cover and let stand for 1 hour to allow the flavours to infuse.
2. Pour the infused cream through a fine mesh strainer to remove the mint, pressing firmly on the leaves to extract as much flavour as possible.
3. Stir in the sugar and salt, and return the infused cream to the stovetop over medium-high heat. Warm the cream until wisps of steam start to rise from the surface.
4. In a medium sized mixing bowl, whisk together the egg yolks, then slowly pour some of the warm mint mixture into the yolks, whisking constantly, then scrape the warmed yolks back into the saucepan.
5. Cook the custard, stirring constantly, until the mixture thickens enough to coat the back of a wooden spoon. Immediately remove from heat, and stir in the remaining 1 cup cream along with the creme de menthe and food colouring, if using.
6. Scrape the custard into a clean mixing bowl, and cover with plastic wrap, placing the wrap directly on the surface of the custard to stop a skin from forming. Chill thoroughly in the refrigerator for at least 2 hours.

Make the Chocolate Chips:

1. While the custard base is chilling, melt the chocolate in the microwave or a double boiler until smooth. Add the oil, and set aside to cool to room temperature.

Freeze the Ice Cream:

1. Using an ice cream maker, freeze the chilled custard as per the manufacturer's directions.
2. To create the chocolate "chips", spoon a layer of ice cream into the container, then drizzle a thin stream of chocolate overtop using a swirling motion. Continue alternating layers of ice cream and chocolate until both of them are done, then swirl the mixture with a butter knife to break up the chocolate into irregular pieces. Cover and transfer to the freezer to chill until firm and scoopable, about 3-4 hours.