Chop the chocolate using a serrated knife. Put ¾ cup (140g) of chopped chocolate in a large heatproof bowl, and set aside. The rest you'll use for the chocolate drizzle later.
Combine the milk and mint in a saucepan. Heat over medium heat until small bubbles form and it starts to steam, about 6 to 7 minutes. Remove from heat and let it steep 20 minutes.
Meanwhile, in a medium bowl, combine the egg yolks, heavy cream, sugar, and salt. Whisk until smooth and the sugar is dissolved.
Temper the egg mixture by slowly adding ½ cup of the warm milk to the egg mixture while continuously whisking. Add another ½ cup of milk and whisk again.
Pour the warmed egg mixture back into the saucepan with the remaining milk. Bring to a simmer over medium heat. Cook until thickened, stirring constantly, about 4 to 6 minutes. It should coat the back of the spoon and leave a trail when you draw your finger through it, but custard should not boil.
Add the hot custard into the bowl with the chopped chocolate. Cover and let sit for 2 minutes, then stir until smooth.
Strain the custard through a fine mesh strainer into a clean bowl, pressing on the mint. Put the chocolate custard bowl in a larger bowl filled with an ice bath (half ice/half water). Stir the custard occasionally until it's cooled to room temperature. Place a piece of plastic wrap on the surface of the custard and refrigerate until chilled, at least 3 hours or overnight.
About 30 minutes before freezing the ice cream, melt the remaining chocolate in the microwave about 1 to 2 minutes, stirring after 30 second increments. Add the canola oil and stir again. Let it cool to room temperature.
Pour the custard into an ice cream maker and freeze per the manufacturer’s instructions. When it’s almost done and has the consistency of whipped cream, pour in the melted chocolate with the machine running. Churn until all the melted chocolate has been added and mixed into the ice cream. Alternatively, stop the machine, pour a little chocolate in, and restart churning. Repeat until all the melted chocolate has been added.
Transfer the ice cream to a freezer-safe container and smooth over using a small offset spatula. Freeze for 2 to 4 hours to allow ice cream to firm up. Serve and enjoy!
I use 1% milk, but you can use whatever you have on hand.For me, dark chocolate is 72% cocoa...bittersweet chocolate has deep flavor, and you don't need the extra sugar because the gelato takes care of that already. If that's too intense, use semi-sweet chocolate instead.I use a KitchenAid Ice Cream Maker Attachment to churn my ice cream. It's actually my older daughter's, a wedding gift she received. She's generously letting me use it on a long-term loan. I also like this ice cream maker (I had one for many years before moving to Boston).