Preheat oven to 375 degrees. Butter 4 (6-8 ounce) ramekins and place on a baking sheet.
Melt the chocolate chips and butter together. Stir until smooth and glossy. Stir in the duck egg yolks, 3 tablespoons sugar, and the vanilla.
Beat the eggs whites with 3 tablespoons of sugar and the salt until stiff peaks form. Stir a large dollop of the egg whites into the chocolate mixture and then fold in the rest. Divide the batter evenly among the prepared ramekins. Bake for 20 minutes or until the tops are lightly cracked but the centers are still gooey – a toothpick inserted into the center should come out with chocolate on it.