In a heavy-bottomed saucepan, whisk together egg yolks, sugar, and coffee until well combined. Whisk in cream and milk until yolk mixture is fully incorporated.
Place pot over medium-low heat and cook, whisking frequently, until a custard forms on a spoon and a finger swiped across the back leaves a clean line, or until custard temperature reaches 170°F. Stir in salt to taste.
Strain custard through a fine mesh strainer and chill in either ice bath or refrigerator until it is very cold, about 40°F. Churn in ice cream maker according to manufacturer's instructions, then transfer to an airtight container and to harden in freezer for at least 4 hours before serving.
