In a medium saucepan, combine the milk, cream, sugar, cinnamon stick, and salt over medium heat just until the liquid starts to steam and you notice small bubbles in the liquid around the edges of the pan, but do not let it come to a simmer.
1 1/2 cups heavy cream, 1 1/2 cups whole milk, 1 cup granulated sugar, 1/4 teaspoon kosher salt, 1 cinnamon stick
Meanwhile, whisk the egg yolks in a separate bowl until light.
4 large egg yolks
When the milk mixture is hot, pour 1 cup of the hot liquid into the beaten egg yolks while whisking to gently warm the eggs without scrambling them.
Pour the tempered egg yolks back into the saucepan with the remaining liquid and continue to cook until the temperature is 170–175°F on an instant-read digital thermometer and is just thick enough to coat the back of the spoon.
Remove from the heat and stir in the vanilla. Let the mixture cool to room temperature for 1 hour to allow the cinnamon stick to infuse the custard base with cinnamon flavor.
2 teaspoons pure vanilla extract
Pour the custard mixture through a fine mesh strainer into a large bowl, discarding the cinnamon stick and whisk in the ground cinnamon. Cover and cool completely in the refrigerator for 4–6 hours until thoroughly chilled.
2 teaspoons ground cinnamon
Once the custard base is thoroughly chilled, pour it into an ice cream maker and churn according to the manufacturer’s instructions.
Transfer the ice cream into a well-chilled freezer-safe container. Cover and place the ice cream in the freezer to cure for 4–6 hours or until the ice cream has hardened.