Preparation:
1. Combine the cream, milk, sugar, vanilla, instant espresso, and cinnamon in a heavy saucepan over medium heat. Cook until the milk is hot but not boiling and the sugar is dissolved, about 10 minutes. Remove the pan from the heat.
2. Place the egg yolks in a bowl and whisk to mix. Whisking constantly, slowly pour in 1 cup of the hot milk mixture and whisk until smooth.
3. Slowly pour the egg mixture into the saucepan, whisking constantly until well combined. Place the saucepan over medium heat and stir the mixture constantly until it is thick enough to coat the back of a spoon, 6 to 8 minutes. The mixture should never boil.
4. Strain the mixture into a bowl and stir in the Tia Maria. Cool to room temperature.
5. Freeze in an ice cream maker according to the manufacturer's instruction | 