Place a medium saucepan over medium heat. Add milk, 1 cup of the heavy cream, sugar and salt and heat until sugar has dissolved.
Pour the remaining 1 cup of heavy cream in a medium bowl. Set a small mesh strainer over the bowl.
Whisk the egg yolks in a separate small bowl and set aside. When the milk mixture is ready, temper the egg yolks by pouring some of the milk mixture into the eggs, whisking constantly so the eggs temper and do not cook into scrambled eggs. Pour the tempered eggs back into the saucepan and whisk constantly. The mixture will be ready when it has thickened and coats the back of a spoon.
Strain the custard into the cold heavy cream and stir to stop the custard from cooking. Chill the mixture thoroughly in the fridge for several hours to overnight.
Add mint extract and food gels to the cooled mixture and stir to combine. Process the custard in an ice cream maker according to the manufacture's instructions.
Once the ice cream has been churned, gently fold in the chocolate chips. Store the ice cream in an airtight container and place in the freezer for 6 hours to overnight.
Notes
Save fat and calorie cutting for later - Ice cream needs a high fat content to create a creamy texture and are rich and delicious. Ice creams made with less fat are icy and gritty.
Chill the custard - The custard needs to be as cold as possible before it goes in the ice cream maker. I usually let it sit overnight in the refrigerator, but at least 6 hours is fine.
Flavourings - Any extracts, alcohol or other flavourings should be added when the custard is cool. If you add them when the custard is hot, their flavours will deteriorate.
Freezer storage - The ice cream is hard when you take it out of the freezer. Just leave it on your counter for a minute or so, and it will soften enough to scoop easily. Adding a bit of alcohol to your ice cream will help it remain soft enough to scoop right out of the freezer.