1. Preheat the oven to 325°. Set four 1/2-cup ramekins in a baking dish. In a bowl, whisk the egg yolks with 2 tablespoons of the sugar until pale. In a small saucepan, bring the cream and milk to a boil. Off the heat, whisk in the chocolates, then the yolk mixture.
2. Pour the custard into the ramekins. Add enough hot water to the baking dish to reach halfway up the sides of the ramekins. Cover with foil and bake for 22 minutes, until the pots de crème are almost set but still slightly jiggly in the center. Transfer the ramekins to a rack and let cool to room temperature. Cover and refrigerate for at least 1 hour.
3. In a small saucepan, cook the remaining 2 tablespoons of sugar and the water over moderate heat until an amber caramel forms, 6 minutes. Stir in the maple syrup.
4. Pour the warm caramel over the chilled pots de crème. Sprinkle each with a few flakes of Maldon salt and serve.