Place chocolate in medium heatproof bowl; set fine-mesh strainer over bowl and set aside.

Whisk yolks, sugar and salt in medium bowl until combined; whisk in heavy cream and half-and-half. Transfer mixture to medium saucepan. Cook mixture over medium-low heat, stirring constantly and scraping bottom of pot with wooden spoon, until thickened and silky and custard registers 175? to 180F. on instant-read thermometer, 8-12 minutes. DO NOT LET CUSTARD OVERCOOK OR COME TO A SIMMER.

Immediately pour custard through strainer over chocolate. Let mixture stand to melt chocolate, about 5 minutes. Whisk gently until smooth, then whisk in vanilla and espresso mixture. Divide evenly among eight 5-oz ramekins. Gently tap ramekins against counter to remove air bubbles.

Cool pots de creme to room temperature, then cover with plastic wrap and refrigerate until chilled, at least 4 hours or up to 72 hours. Before serving let pots de creme stand at room temperature 20-30 minutes.

WHIPPED CREAM:

Chill mixer bowl and beaters or whisk attachment for stand mixer in freezer at least 20 minutes. Put cold cream, sugar and vanilla in cold mixing bowl and beat on low speed until bubbles form, about 30 seconds. Increase speed to medium and beat about 30 seconds. Increase mixer speed to high and beat until cream is nearly doubled in volume and soft peaks form, 30-45 seconds longer.

Place about 2 tablespoons of whipped cream on each pots de creme. Garnish with a sprinkling of cocoa powder or chocolate shavings if desired.