When you put this caramel custard icing in your mouth, it feels, at least to me, as if you were enjoying a mixture of caramel pudding, dulce de leche and flan. It is so delicious and decadent, yet light and, believe me or not, not too sweet. You can use it to fill and cover a cake, or it can be eaten on its own as a caramel pudding. This icing is similar, based on comments online, to the icing used in the Philipines’s famous caramel cake called “Estrel Caramel Cake,” which is a 2 layer chiffon cake filled and covered with a caramel pastrycream-like caramel icing. This (slightly adapted) recipe that I am sharing here comes from a food blog called “Heart of Mary” @ pinoyinoz.blogspot.com. Both the Estrel bakery in the Philippines and “Heart of Mary” have a way of pouring the icing, without using any utensils, on the cake in an uniform way so that the icing looks ultra smooth and glossy. This process is still a trial and error thing for me as I was able to do it once fairly well (see 1st pic) but the second time (see 2nd pic), it did not look too good so I ended up using a fork to draw lines over the cake. Either way is fine since the taste and texture of the icing does not change, but if you don’t want to experiment with trying to pour icing over the cake, do like me. Refrigerate the icing first and then spread it on the cake like with any other buttercream. I then like to use a fork to draw lines all over the cake. Or just place warm icing in individual ramekins and refrigerate until set —Regine
Whisk the egg yolks with 3 tablespoons of the sugar in a small bowl. Add in 6 tbsp of the evaporated milk and cornstarch. Mix well, then set aside.
In a heavy saucepan, over low to medium heat, caramelize the remaining sugar. When sugar is completely melted and a golden brown color, add boiling water. Please note that the darker the color, the more pronounced the caramel flavor and color will be but you want to be careful since you don’t want it to be too dark. Bring back to a boil, making sure all the caramel is incorporated into the water.
Carefully add in the rest of the evaporated milk; when it starts boiling take maybe 2 big spoonfuls of the caramel/milk mixture and add it to the egg mixture in order to temper the eggs. Mix until incorporated, then pour the egg mixture into the caramel mixture
Mix until it reaches a thick consistency but it is still pourable. This is, I admit, where it can be tricky since you may not necessarily know when you have reached the optimal consistency. But I think you want the mixture slightly less thick than condensed milk. Remove from heat and then add the butter and vanilla. Let cool for 5 minutes, stirring occasionally. At this point, if you want to do like the Estrel bakery or “Heart of Mary,” you want to pour it while still warm over the cake, and let it flow smoothly over the top and sides of the cake. I know they also fill the cake with it and I have no idea as to how they can do that without the 2 layers sliding. So this is why in my case I instead choose to place the icing in the refrigerator, maybe for a couple of hours, and then I fill and frost the cake. Or place icing in individual ramekins and set in the refrigerator.