Place 4 (6 ounce, 170 milliliter) ramekins in a deep, large baking dish and set aside.
Preheat oven to 325˚F (160˚C).
In a small saucepan, place the heavy cream over medium heat.
Once the cream begins to steam, but not boil, remove from heat.
While the cream is heating, melt the dark chocolate in a double boiler or in the microwave at 20 second intervals, stirring often, until smooth.
In a medium bowl, whisk together the granulated sugar, egg yolks, and salt until light and thickened.
While whisking the eggs, slowly add the heavy cream in a thin stream, careful not to heat the eggs too quickly or beat too much air into the mixture. If any of the eggs scramble, strain the mixture.
Whisk in the melted dark chocolate until smooth, followed by the vanilla extract.
Divide the custard evenly among the ramekins. Carefully fill the pan halfway up the ramekins with hot water without splashing any into the ramekins.
Gently transfer the pan to the preheated oven without splashing any water. Bake until set, but still a little loose in the center, 30-40 minutes.
Carefully remove the ramekins from the baking dish and allow to cool to room temperature on cooling rack.
Cover and refrigerate 4 hours to overnight.
Once ready to serve, top each custard with an even layer of sugar, about 1 tablespoon (12 grams). Move the flame from a culinary torch across the entire surface until the sugar starts to darken and caramelize.
Serve immediately with desired toppings such as whipped cream, cacao nibs, sprinkles, strawberries, and fresh mint.