FOR THE CAKE BATTER:

Preheat oven to 425 degrees F. Butter and lightly flour six 4-ounce ramekins or custard cups. Tap out the excess flour and refrigerate the molds for 15 minutes to set the butter.

Melt the butter and chocolate in the top of a double boiler over simmering water. Remove from heat and let cool slightly.

In the bowl of an electric stand mixer fitted with the paddle attachment, beat together the whole eggs, yolks, and the sugar on medium-high speed until light and thick. Add the melted chocolate mixture and beat to combine. Mix in the 1 tablespoon flour until just combined. Transfer to a large bowl.

Wash and dry the mixing bowl, add the egg whites, and whip on medium speed until soft peaks form. Fold the whites into the chocolate mixture. Fill each ramekin halfway with the batter. Place 1 heaping tablespoon of the dulce de leche in the center and then top with the remaining batter.

Place the ramekins on a baking sheet, and bake until the sides have set but the centers remain soft, 6 to 7 minutes.

Run a small knife around the perimeter of each cake to loosen slightly and then invert each mold onto a plate to unmold. Serve with ice cream and hot fudge sauce.

FOR THE DULCE DE LECHE:

Combine the milk, coconut milk, corn syrup, sugar, cinnamon sticks, and vanilla bean and seeds in a medium saucepan and bring to a boil over medium-high heat. Dissolve the baking soda in a small bowl with a few tablespoons of water and whisk into the milk mixture. Cook the mixture, stirring occasionally, until reduced by half and caramelized, 8-10 minutes.

Remove the vanilla bean, transfer the mixture to a bowl, and refrigerate until firm, about 2 hours. This will keep, tightly covered, in the refrigerator for up to 1 week.