10 ounces bittersweet chocolate (60%, if using 70% the chocolate needs to be reduced to 8 ounce)
5 lrg egg yolks
5 Tb sugar
1/4 ts salt
1 1/2 c heavy cream
3/4 c half and half
1 Tb vanilla extract
1/2 ts instant espresso powder mixed with 1 Tb water
Place chocolate in a medium heat proof bowl; set a fine mesh strainer over the bowl and set aside.
Whisk yolks, sugar and salt in a 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 the bottom of the pot with wooden spoon, until thickened and silt and the custard registers 175F - 180F on instant read thermometer. Do not let the custard overcook or simmer.
Immediately pour the custard through strainer over chocolate. Let mixture stand to melt the chocolate, about 5 minutes Whisk gently until smooth, then whisk in the vanilla and espresso. Divide mixture evenly amount eight 5 ounce ramekins. Gently tap ramekins against counter to remove air bubbles.
Cool pots de creme to room temperature, then cover with cling and refrigerate until chilled, at least 4 hours or up to 72 hours.Before serving let pots de creme stand at room temperature for 20 - 30 minutes. Serve with sweetened whipped cream.