Last week I made a Mexican chocolate cake for my dad's birthday. I took from many recipes to make it and had a little meltdown because the filling would not thicken. After adding some cornstarch and putting it in the freezer it finally became usable; though it still was like a thick pudding and soaked a little into the cake. It was really good and even better a couple days later when we came to visit.
For the cake I used this recipe, the filling (though it was super runny so be cautious), and for the frosting I used the chocolate butter cream from Vegan Cupcakes Take Over the World and added cinnamon to it. I then made a dulce de leche by cooking sweetened condensed milk on a double boiler (if I couldn't get the filling to thicken I was planning on using it as the filling, so I had two options). I also sprinkled gold sugar on top of it as well.