Note: Make sure to freeze the base of your ice cream maker overnight before making this recipe.

1. In a medium saucepan, slowly whisk the cornstarch into 1 cup cold whole milk, then whisk in the sugar. Apply medium heat and heat for 4 to 6 minutes, whisking frequently, until nearly simmering and the mixture thickens.
2. Remove from the heat. Stir in the remaining ½ cup whole milk, heavy cream, salt, peppermint extract, vanilla extract, and green food coloring. 
3. Transfer the mixture to a large metal or glass bowl. Place the bowl in a smaller bowl of ice water for 1 hour, making sure not to splash any water into the ice cream (or even quicker, you can pour it into a 1-gallon zip-top bag, seal it, and place the bag in ice water for 30 minutes). Alternatively, simply place the bowl in the refrigerator and wait for 3 to 4 hours or until the temperature drops to 40 degrees Fahrenheit.
4. Churn according to your ice cream maker instructions, about 25 minutes for soft serve consistency.
5. When the ice cream is done churning, place the chocolate chips and oil in a dry glass measuring cup or bowl (make sure the cup or bowl are perfectly dry or the chocolate will seize). Microwave on High power for 30 seconds, then stir. Microwave another 30 seconds and stir. At this point it should be mostly melted with a few unmelted chunks: keep stirring until all the unmelted bits disappear and the chocolate is perfectly smooth. (If not, microwave in 10 second bursts until it is mostly melted.) You can also melt the chocolate on the stove on a double boiler: remove it from the heat just when the larger bits of chocolate melt.
6. Transfer the churned ice cream into a loaf pan or storage container. Drizzle about 1/6 of the chocolate in lines over the entire surface, then wait for a few seconds until it starts to solidify. Use a spoon to stir the chocolate into the ice cream, creating irregular chocolate chunks and spreading them evenly throughout. Do this about 6 times until the entire amount of chocolate is incorporated. (It’s helpful to drizzle in lines and not one large chunk, which solidifies quickly and can be difficult to break apart. You can break up any very large chunks into smaller pieces using a spoon if you like.) The ice cream may melt a bit, which is expected: stir to incorporate everything and smooth the top into an even layer. 
7. Place the container in the freezer and freeze for at least 2 hours (or up to 4 hours), which “ripens” the ice cream and creates the hard ice cream texture. Store in a loaf pan with a parchment sheet over the top or a sealed container in the freezer for up to 2 weeks.