In this recipe, dulce de leche is made using sweetened condensed milk, but it can also be made from scratch or bought already prepared. A couple popular brands of dulce de leche available in Argentina are La Serenísima and La Salamandra for fancier tastes. Dulce de leche has its origins in both Europe (known as confiture de lait) and South America, and has become more popular in the United States within the past ten years.
10 – 12 Servings:
For the Dulce de Leche
Pour the cans of sweetened condensed milk into the top pan of a double boiler and place over boiling water and cover. Let the milk simmer, covered, stirring occasionally, until it has a light caramel color. This takes about 2 1/2 to 3 hours. Make sure to add more water to the bottom pan as it cooks away. While you are waiting for the milk to cook you can prepare the cake.
For the cake
Preheat the oven to 375 degrees F.
Grease a 15 1/2" by 10 1/2" jelly roll pan. Line it with waxed paper cut to the size of the pan, and then grease the waxed paper and dust it with flour, tapping out any excess.
Combine the flour, cocoa and salt.
In a small bowl, beat the egg whites on high speed with the cream of tartar until doubled in size. Then, while beating on high speed, add 1/4 cup of the sugar and beat until it is completely dissolved and the mixture becomes somewhat stiff.
In a large bowl, beat the egg yolks and the remaining 1/4 cup of sugar until completely dissolved and thick.
With a rubber spatula, carefully fold the beaten egg whites into the egg yolk mixture. Next, carefully fold the flour mixture into the egg mixture with the rubber spatula. Finally, fold in the melted butter until just combined.
Spread the batter evenly in the prepared cake roll pan and bake in the center rack of the oven for 10-12 minutes, or until the top of the cake springs back when touched.
Sprinkle a clean cloth towel with the powdered sugar. When the cake is done cooking, invert it immediately onto the prepared towel and remove the waxed paper from the bottom. Starting from one of the long edges, roll the cake length-wise in the towel, jelly-roll fashion. Let the roll cool for about an hour, with the seam side down.
To prepare the cake roll
When the cake has cooled and the dulche de leche is done, gently unroll the cake and generously spread the filling on the inside of the cake, almost to the edges. Then, gently roll the cake back up and hold it for a few seconds. With a sharp knife, carefully cut the ends of each side of the cake, and if desired cut the cake in the middle to have two separate pieces. Gently spread the remainder of the dulce de leche on the outside of the cake. Stick toothpicks into the cake, cover with plastic wrap, and chill.
When the cake is sufficiently chilled, cut it into round slices, and serve. The cake can be kept covered in the refrigerator until ready to serve.