Set your oven rack to the middle position and preheat the oven to 325 degrees. Grease the sides and bottom of 6 coffee cups* (8 ounce capacity) with the extra butter. Set them in the bottom of a deep roasting pan. Bring a kettle of water to boil.
Add the bittersweet, Mexican chocolate, cinnamon and ancho powder into the food processor. Pulse until the chocolate is ground into very small pieces. Transfer the chocolate into a large mixing bowl.
In a small pot set over medium heat, bring the stick of butter to a boil. Remove from the heat and pour the melted butter over the chocolate. Stir until all the chocolate has melted and the mixture is smooth. Add the Kahula and blend it into the chocolate.
Beat the eggs in an electric mixer using the whisk attachment on high speed for 5 minutes. Using a large rubber spatula, gently fold the egg mixture into the chocolate mixture in three stages.
Divide the batter evenly between the prepared cups. I find that using a ladle make this step easier. Smooth out the tops. Set the roasting pan into the oven and pour enough hot water to come about halfway up the sides of the cups. Bake until the top of the cake has set and the edges are just beginning to pull away from the sides, 22 - 25 minutes. The cake will continue to firm up as it cools. Remove the cups from the water bath and set on a wire rack to cool to room temperature. Cover and refrigerate until ready to serve.
When ready to serve, place the cup on a saucer. Whisk together the crema and sugar. Add a dollop of the sweetened crema to the top of each cake and top it with a sprinkle of grated Mexican chocolate.
* Cook’s Note: It’s important when choosing a coffee cup for this recipe that the cup isn’t tapered too much. It should be close to the same size on the top as it is on the bottom so that the cake bakes evenly.
Advance Preparation: You can prepare the cake batter, fill the cups, hold them covered with plastic in the refrigerator for up to 4 hours before baking. Follow baking instructions, but increase the baking time to 28 to 30 minutes. Once baked, they’ll last several days in the refrigerator wrapped in plastic.