In a medium saucepan, combine heavy cream, whole milk, sugar, and instant coffee powder. Heat over medium heat, stirring occasionally, until sugar and coffee dissolve and mixture is hot but not boiling.

In a separate bowl, whisk egg yolks and salt until pale and slightly thickened.

Slowly pour about half the hot cream mixture into the egg yolks, whisking constantly to temper the eggs.

Return the egg yolk mixture to the saucepan with remaining cream mixture.

Cook over low heat, stirring constantly until custard thickens enough to coat the back of a spoon (~170°F/77°C). Do not boil.

Remove from heat; stir in vanilla extract.

Strain custard through a fine-mesh sieve into a clean bowl to remove any cooked egg bits.

Cool to room temperature, then refrigerate at least 4 hours or overnight until fully chilled.

Pour chilled custard into ice cream maker; churn according to manufacturer instructions until thick and creamy.

Transfer ice cream to container; freeze at least 2 hours before serving.