In a medium mixing bowl, whisk together 6 egg yolks and ¼ cup granulated sugar until pale and smooth, about 2-3 minutes. Gradually pour in 1 cup of heavy cream and 1 cup of whole milk, whisking continuously to combine.

Pour the combined custard mixture into a saucepan and place it over medium heat. Stir constantly for about 5-7 minutes until the mixture is warm but not boiling.

Remove the saucepan from heat, and place 6 oz of chopped bittersweet chocolate in a large mixing bowl. Pour the warm custard over the chocolate in a slow and steady stream, whisking continuously until smooth and fully combined, about 2-3 minutes.

Carefully pour the chocolate mixture into individual jars or ramekins, filling them about three-quarters full. Allow them to cool at room temperature for about 10-15 minutes, then cover the containers with plastic wrap and refrigerate for at least 2-3 hours, or until set.

Once the chocolate budino is set, remove it from the refrigerator and uncover it. Top each budino with espresso cream and a sprinkle of flaky salt right before serving.