In a medium saucepan, combine heavy cream and whole milk. Heat over medium flame, whisking gently until small bubbles form around the edges, about 5-7 minutes, then remove from heat.

In a separate bowl, whisk four egg yolks until smooth. Slowly pour half of the hot cream mixture into the yolks, whisking continuously to prevent curdling.

Pour the tempered egg mixture back into the saucepan with the remaining cream and milk. Over medium-low heat, stir continuously for about 2-3 minutes, until the mixture thickens slightly.

Remove the saucepan from heat and stir in the chopped semisweet chocolate, optional espresso powder, and a pinch of kosher salt.

Strain the chocolate mixture through a fine mesh sieve into a clean bowl, discarding any lumps. Evenly distribute the mixture into six 4-ounce ramekins. Cover and refrigerate for about 2 hours.

Let the individual pots sit at room temperature for about 15 minutes before serving. Garnish with whipped cream and chocolate shavings.