Instructions

for the pots de crème

Place chocolate and vanilla in a small bowl and set fine-mesh strainer over bowl; set aside. Whisk sugar, egg yolk, and salt in a small saucepan until smooth and pale yellow, about 30 seconds, taking care to thoroughly scrape mixture from corners of saucepan. Gently whisk in cream and espresso powder until evenly combined.
Cook cream mixture over low heat, stirring vigorously and scraping bottom of saucepan with silicone spatula (do not whisk), until sugar is fully dissolved, about 1 minute. Increase heat to medium-low and continue to cook, stirring constantly with spatula, until mixture is slightly thickened and registers 175 degrees, 1 to 2 minutes longer. (Mixture should steam but not simmer; adjust heat as needed to keep mixture from heating too quickly.)
Immediately strain mixture through prepared strainer into bowl with chocolate. Let sit until chocolate is softened, about 1 minute, then vigorously whisk until chocolate is fully melted and mixture is smooth, about 1 minute, scraping down sides of bowl as needed.
Divide mixture between 2 small (approximately 4-ounce) ramekins, jars, or cups. Gently tap ramekins against counter to release air bubbles. Let cool to room temperature, about 15 minutes, then cover with plastic wrap and refrigerate until well chilled, at least 2 hours or up to 3 days.

for the whipped cream

Using a whisk or handheld mixer at medium-low speed, whip cream and sugar in a bowl until soft peaks form, 1 to 3 minutes.
Dollop each pot de crème with about 2 tablespoons whipped cream. Serve.