For the eggshells, carefully remove the tops from the eggs with an egg top cutter or a sharp paring knife. Pour out the eggs; reserve 3 of the yolks—1 for the pots de crème, 2 for the caramel foam. Rinse the shells in very hot water, carefully removing the membrane remaining inside the shells. Allow the shells to dry completely.

For the pots de crème, preheat the oven to 350°F.

Whisk the yolk and sugar together in a small bowl. Combine the milk and heavy cream in a small saucepan and bring to a boil. Gradually whisk the milk mixture into the egg mixture. Whisk in the chocolate until it is melted and well incorporated. Strain the custard through a fine-mesh sieve into a bowl and cool it quickly over an ice bath, stirring occasionally.

Stand the eggshells in a fiberboard egg carton and put the carton in a baking dish. Divide the custard evenly among the eggshells, filling each one about halfway. Fill the baking dish with enough hot water to reach halfway up the sides of the egg carton. Cover the dish with aluminum foil and bake the pots de crème for 15 to 20 minutes, until the custard is set. Allow the pots de crème to cool to room temperature, then refrigerate.

For the caramel foam, combine the sugar and water in a small saucepan and cook, without stirring, over medium heat until the sugar has dissolved and the caramel turns a light golden brown.

Meanwhile, whisk the egg yolks together in a bowl. Heat the heavy cream and milk together until hot. Remove the caramel from the heat and whisk in the cream mixture. Whisk the mixture over low heat until any lumps of caramel have completely dissolved and the caramel is smooth. Gradually whisk the caramel into the egg yolks, and return to the saucepan. Cook the sauce over low heat until it reaches 183°F. Remove from the heat and add the gelatin, whisking until it dissolves. Strain through a fine-mesh sieve into a bowl and chill in an ice bath, then refrigerate until ready to use.

To serve, place the filled eggshells in four porcelain egg cups, and drizzle 1/4 teaspoon of the caramel sauce over each pot de crème. Take the caramel foam out of the refrigerator and transfer it to a whipped cream dispenser. Fill the shells with caramel foam, leaving a little indentation in the center. Drizzle 1/8 teaspoon of the maple syrup into each indentation, and sprinkle each pot de crème with a few grains of Maldon sea salt.

Serve immediately.

For the Caramel Sauce

In a small pot, combine the sugar, corn syrup, lemon juice, and water. Without stirring, cook the mixture over medium heat until the sugar has dissolved and the caramel turns a golden color.

Meanwhile, heat the heavy cream in a separate pot until warm.

Remove the sugar mixture from the heat and quickly whisk in the cream (the sugar mixture and the cream should be warm to avoid lumps from forming). Whisk the sauce over low heat until the sugar is completely dissolved and the sauce is smooth.

Remove the sauce from the heat and whisk in the butter.

Allow the sauce to cool, transfer to a container, and cover tightly with plastic wrap. Store at room temperature if using the same day or refrigerate until ready to use, up to 1 week. Makes about 1/2 cup.