Step 1: Preheat oven to 325°F (160°C). Place 4 ramekins in a large baking dish.
Step 2: In a saucepan, heat cream and sugar over medium heat until steaming but not boiling, stirring to dissolve sugar.
Step 3: Remove from heat, add chopped chocolate, and whisk until completely melted and smooth.
Step 4: In a separate bowl, whisk egg yolks and vanilla until pale and slightly thickened.
Step 5: Slowly pour the warm chocolate cream into the egg yolks while whisking constantly to prevent curdling.
Step 6: Strain the mixture through a fine-mesh sieve into a pouring jug to ensure smoothness.
Step 7: Divide the mixture evenly among the ramekins.
Step 8: Pour hot water into the baking dish until it reaches halfway up the sides of the ramekins.
Step 9: Bake for 30-35 minutes until edges are set but centers still jiggle slightly.
Step 10: Remove ramekins from water bath, cool to room temperature, then refrigerate for at least 4 hours or overnight.
Step 11: Before serving, sprinkle a thin, even layer of sugar (about 1 tbsp per ramekin) over each custard.
Step 12: Caramelize the sugar using a kitchen torch until golden brown and crisp, or broil for 1-2 minutes watching carefully.
Step 13: Let sit for 1-2 minutes to harden the sugar crust before serving.