Brazo Gitano with Ponche Crema Sauce

steps

1. Make the dulce de leche: In a small saucepot filled with water, boil unopened can of sweetened condensed milk in water for about 31⁄2 hours. (Ensure the pan always has enough water to cover the can.) Carefully remove can from pot (it will be hot) and let cool 1 hour before opening.
2. Make the brazo gitano: While dulce de leche is cooling, preheat oven to 325 degrees. In bowl of a stand mixer fitted with whisk attachment, whip egg whites until frothy. Add sugar and whip on medium speed until stiff peaks form.
3. In a separate bowl, whisk egg yolks until thickened; stir in vanilla.
4. To meringue add cake flour, salt, and baking powder. Fold gently until combined. Add yolk mixture and fold to combine.
5. Line a half-sheet tray with parchment paper and spray the top and sides with cooking spray. Pour batter into the tray and spread evenly. Bake 10 minutes. Let cool slightly.
6. While cake is still warm, lightly dust with powdered sugar. With a knife or bench scraper, cut down the sides and corners to ensure complete release. Stretch a piece of plastic wrap across pan and flip cake over onto table to transfer cake to plastic wrap. Remove pan.
7. With an offset spatula evenly spread 3⁄4 cup dulce de leche over cake. Sprinkle with Maldon sea salt.
8. Start rolling cake, ensuring the first roll is tight. When entire cake is rolled, cover tightly with plastic wrap to hold the shape and refrigerate for 20 minutes.
9. Make the ponche crema sauce: In a small saucepot, heat whole and evaporated milks over low heat.
10. In bowl of a stand mixer fitted with paddle attachment, beat egg yolks until they turn white. Add to milk along with vanilla bean seeds and nutmeg. Stir constantly with a spatula over low heat to prevent egg yolks from coagulating, until the mixture thickens, between 156 and 181 degrees.
11. Let cool for 15 minutes, stirring occasionally, then strain. Add 3⁄4 cup sweetened condensed milk and stir in rum and salt. Pour over cake and cut into slices.