To make the ice cream, combine the cream, milk, sugars, and salt in a medium saucepan over medium heat. Put the egg yolks in a medium bowl nearby and whisk them gently. Bring the milk/cream mixture to a simmer, then when it just starts to come to a boil, remove the pan from the heat. Whisk the egg yolks while you slowly pour in about a third of the hot cream mixture, whisking constantly so the eggs heat up but don’t cook during the process.
Now return the saucepan to the heat and start whisking the cream while you pour in the hot egg mixture. Continue to whisk as the custard cooks, and cook it until it thickens slightly and coats the back of a spoon. If you want to use a candy thermometer, you’re shooting for 175 F (80C).
Take the pan from the heat and strain the ice cream custard through a fine mesh strainer into a bowl. Whisk in the vanilla extract and ground cinnamon, then continue to whisk occasionally as it cools. Once at room temperature, press a layer of cling wrap on top of the custard and refrigerate it until it’s completely chilled. (To speed up the process, you can place the bowl over an ice bath and whisk it as it cools down.)
While the custard chills, prepare the cinnamon crunch. Microwave the cinnamon chips for 25 seconds, then stir until melted, heating them again in short intervals if necessary. If your melted chips are still fairly stiff, add a little coconut oil or vegetable oil, just so that they’re smooth and fluid when melted. Pour the melted cinnamon chips over the crispy rice cereal and stir until the cereal is well-coated. Scrape the cereal out onto a baking sheet lined with waxed paper and spread it into a thin, even layer. Refrigerate until set, then use a knife or your fingers to crumble the cereal mixture into small pieces.
When the custard is chilled and the cinnamon crunch is ready, place a 9x5 loaf pan in the freezer. Churn the ice cream according to your ice cream maker’s instructions. Once finished, add the cinnamon crunch and stir it in. Scrape the ice cream into the loaf pan and smooth it into an even layer. Cover the ice cream with cling wrap, and return to the freezer to firm up completely.