Step 1Whisk together the egg yolks in a small bowl. Place the finely chopped chocolate in a large glass or plastic bowl.
Step 2In a medium, heavy-bottom saucepan, combine the milk, cream, corn syrup and orange zest. Bring the mixture to a boil over high heat. When it has come to a boil, remove from heat and whisk one-half cup of the milk mixture into the eggs. (This will warm, or "temper," the eggs.)
Step 3Stir the tempered egg mixture back into the saucepan with a wooden spoon and heat over medium heat. Cook, stirring constantly, just until the mixture thickens to a custard and will coat the back of the spoon. Immediately remove from heat and strain the custard into the bowl containing the chocolate.
Step 4Quickly stir the custard with the chocolate until the chocolate is completely melted and the mixture is smooth. Divide the custard between each of 4 individual serving bowls or glasses. Refrigerate the bowls, uncovered, until the custard is set (a pudding-like consistency), a couple of hours up to overnight.
Step 1In a medium, heavy-bottom saucepan, combine the sugar with the water. Bring the mixture to a boil over medium-high heat and continue to cook until the sugar caramelizes to a rich golden color. Be careful not to overcook or the sugar will burn.
Step 2Meanwhile, in a small saucepan, bring the cream and milk to a boil. As soon as the sugar caramelizes, remove from heat. Immediately whisk the milk mixture into the caramel, but be very careful as the mixture will steam and this could burn. Once the mixture is smooth, stir in the salt and bring the mixture to a boil over high heat.
Step 3While the caramel mixture is coming to a boil, whisk together the egg and cornstarch in a medium bowl, then whisk in the rum. When the caramel mixture has come to a boil, remove from heat and whisk one-half cup into the egg mixture to temper the eggs.
Step 4Whisk the tempered egg mixture back into the saucepan and heat over medium heat, whisking constantly, until the mixture thickens to a custard consistency, 1 to 2 minutes. Immediately remove from heat and strain into a medium bowl. Remove the chilled chocolate custards from the refrigerator.
Step 5Gently pour the caramel custard evenly into the 4 chilled serving bowls, forming a layer over each of the chocolate custards. Refrigerate, uncovered, until chilled.
Step 6Serve each custard with a dollop of whipped cream and a sprinkling of fresh berries.