01 - Combine whole milk, heavy cream, half the sugar, and salt in a medium saucepan. Heat over medium heat until just steaming, avoiding a boil.
02 - Whisk egg yolks with remaining sugar in a separate bowl until mixture becomes pale and thickened.
03 - Gradually pour about 1 cup of hot milk mixture into yolks while whisking continuously to prevent curdling.
04 - Return yolk mixture to saucepan. Cook over medium-low heat, stirring constantly with a wooden spoon, until custard thickens and coats the back of the spoon, reaching 170–175°F, approximately 4–6 minutes.
05 - Remove from heat. Stir in brewed coffee, instant espresso powder if using, and sweetened condensed milk until completely blended.
06 - Pour custard through a fine-mesh sieve into a clean bowl. Cool to room temperature, then cover and refrigerate until thoroughly chilled, minimum 4 hours or preferably overnight.
07 - Process chilled custard in ice cream maker according to manufacturer instructions until thickened.
08 - Transfer churned ice cream to an airtight container. Freeze for at least 2 hours before serving to achieve firmer consistency.