In a medium saucepan, combine the whole milk, heavy cream, and half of the sugar (3/8 cup). Warm over medium heat, stirring occasionally, until the sugar dissolves and the mixture is steaming but not boiling.

In a separate medium bowl, whisk the egg yolks with the remaining sugar (3/8 cup) and salt until the mixture is pale, thick, and ribbony.

Slowly pour about one cup of the warm milk mixture into the egg yolk mixture while whisking constantly. This is called tempering and prevents the eggs from scrambling.

Pour the tempered egg mixture back into the saucepan with the remaining milk. Cook over low-medium heat, stirring constantly with a wooden spoon or spatula, scraping the bottom and sides. Continue until the custard thickens enough to coat the back of the spoon (about 5-7 minutes). Do not let it boil.

Remove the saucepan from the heat and stir in the cooled espresso. Pour the custard base through a fine-mesh sieve into a clean bowl to ensure a silky-smooth texture.

Cover the bowl with plastic wrap, pressing it directly onto the surface of the custard to prevent a skin from forming. Refrigerate for at least 4 hours, but preferably overnight.

Once thoroughly chilled, pour the base into your ice cream maker and churn according to the manufacturer's instructions until it reaches a thick, soft-serve consistency. For the no-churn method, pour the base into a freezer-safe container. Freeze for 45 minutes, then stir vigorously. Repeat every 30 minutes for 3-4 hours.

Transfer the churned gelato to an airtight, freezer-safe container. Press parchment paper on the surface and freeze (ripen) for at least 2-3 hours to firm up. Let it sit at room temperature for 5-10 minutes before scooping and serving.