01 - Combine whole milk, heavy cream, half the sugar, and salt in a medium saucepan. Heat over medium heat until just steaming, not boiling.
02 - Whisk egg yolks with remaining sugar in a separate bowl until pale and thickened.
03 - Slowly pour about 1 cup of hot milk mixture into yolks while whisking constantly to temper the eggs.
04 - Return yolk mixture to saucepan. Cook over medium-low heat, stirring constantly with wooden spoon until custard thickens and coats back of spoon (170–175°F), about 4–6 minutes.
05 - Remove from heat. Stir in brewed coffee, instant espresso powder if using, and sweetened condensed milk until fully blended.
06 - Pour custard through fine-mesh sieve into clean bowl. Cool to room temperature, then cover and refrigerate until thoroughly chilled (at least 4 hours, preferably overnight).
07 - Churn custard in ice cream maker according to manufacturer's instructions.
08 - Transfer to airtight container and freeze for at least 2 hours before serving for firmer texture.