Powdered sugar, for dusting Special Equipment: Mixer with whisk attachment and 8 (4-ounce) ramekins Preheat the oven to 400 degrees F. Coat 8 (4-ounce) ramekins with butter. Add the 1 tablespoon of sugar into 1 ramekin. Swirl to coat, then tap out the excess sugar into another ramekin. Repeat the process until all of the ramekins have been coated. Set aside.
In a double boiler, over low heat, add the remaining 8 tablespoons of butter and the chocolate, stirring occasionally, until melted and combined. Fold in the vanilla extract, cinnamon, and salt. Set aside. In the bowl of a stand mixer, fitted with a whisk, add the eggs, egg yolk, and the remaining 1 cup of sugar. Whisk on medium until the eggs triple in volume. Gently fold in the chocolate mixture. Sift the flour into the bowl and gently fold to incorporate, being careful not to deflate the eggs. Pour the batter into the ramekins, dividing evenly. Arrange the ramekins on a sheet tray. Bake until the tops are set but the center wiggles slightly when lightly shaken, about 18 to 20 minutes. Serve immediately, dusted with powdered sugar.