Whisk the egg yolks. Separate the 4 egg yolks and place them in a mixing bowl with the ground cinnamon and vanilla extract. Whisk together, then set aside.

Warm the cream mixture. In a medium saucepan, combine the whole milk, heavy cream, sugar, and a pinch of salt. Whisk over medium heat until the sugar has dissolved and the mixture is warm, but not scalding. Then reduce the heat to low.

Temper the eggs. Remove about 1 cup of the warm cream mixture and very slowly pour it into the bowl with the egg yolks while whisking continuously.

Combine mixtures. Very slowly pour the tempered egg mixture back into the saucepan, whisking constantly.

Cook the ice cream base. Turn the heat up to medium and cook the ice cream base, while continuing to whisk frequently, until it reaches 170°F. Be careful not to take it too much above this temperature as it can curdle.

Chill the mixture. Remove immediately from heat and pour into a heat-safe container. Cover the container and refrigerate for at least 4 hours or overnight to chill completely.

Churn the ice cream. Once the custard has chilled completely, give it a stir and pour it into your ice cream maker. Churn according to the manufacturer's instructions, usually around 20 minutes, until the texture is thick and creamy.

Serve or store. You can serve the ice cream immediately as soft-serve, or transfer it to an airtight container and freeze for a few hours to firm up. Then scoop, serve, and enjoy!