Chocolate Espresso Pots De Creme

60z bittersweet chocolate, finely chopped
1 1/3 C heavy cream
2/3 C whole milk
1 1/2-2 tsp instant espresso powder
6 large egg yolks
2 Tbsp sugar

Put oven rack in middle position and preheat oven to 300. Put chocolate in heatproof bowl. Bring cream, milk, espresso powder (to taste) and a pinch of salt just to a boil in a small heavy saucepan, stirring until powder is dissolved, then pour over chocolate, whisking until chocolate is melted and mixture is smooth. Whisk together yolks, sugar, and a pinch of salt in another bowl, then add warm chocolate mixture in a slow stream, whisking constantly. Pour custard through a fine-mesh sieve into a 1qt glass measure and cool completely, stirring occasionally, about 15 minutes. Line bottom of a baking pan (large enough to hold ramekins) with a folded kitchen towel and arrange ramekins on towel. Poke several holes in a large sheet of foil with a skewer. Divide custard among ramekins, then bake custard in a hot water bath, pan covered tightly with foil, until custards are set around edges but still slightly wobbly in centers, 30-35 minutes. Transfer ramekins to a rack to cool completely, uncovered, about 1 hour. Chill, covered, until cold, at least 3 hours. Top with chocolate curls.