Ube Custard:

In a double boiler set up over low heat, whisk together 10 egg yolks, 1/2 a can of sweetened condensed milk, 1 cup of whole milk, 1 tbsp of ube extract, 1 cup of ube halaya, 4 tbsp of unsalted butter, and an optional 2 to 3 drops of purple food coloring.

Cook on low heat to prevent the egg yolks from curdling, whisking regularly, for about 30 to 40 minutes, or until the mixture thickens into a spreadable paste. Note: do not overcook - if it becomes too thick, it will be difficult to spread the mixture later.

Meringue:

Preheat your oven to 350 F (175 C) and line a 13" x 18" sheet pan with an oversized piece of parchment paper, so that the parchment paper folds up all 4 sides of the pan, with the edges creased, creating a sharp rectangle.

In a metal or glass mixing bowl (avoid plastic, which can absorb fat and prevent egg whites from increasing in volume), add in 10 egg whites and beat them till they are foamy, about 1 minute.

Then add in 1 tsp of cream of tartar, and continue beating till the egg whites start to turn opaque and begin to fluff into a thick foam.

Then slowly add in 3/4 cup of granulated sugar in small amounts, and continue to beat while gradually increasing the speed of your mixer to medium-high. Continue beating until you see soft peaks form. The whipped egg whites should look smooth and glossy, and you shouldn't be able to feel any sugar grains anymore. Note: Do not overbeat. You only want *soft* peaks, not stiff peaks like with a pavlova. Stop beating at the soft peak stage.

Take the prepared parchment paper-lined sheet pan and add a little of the meringue to 4 corners at the bottom of the parchment paper to prevent it from sliding around.

Transfer the meringue onto the prepared baking sheet and using a spatula, spread it evenly across into about a 1/4-inch-thick layer, flattening it out as much as possible - so that it browns evenly.

Bake it in the preheated oven at 350 F (175 C) for about 20 minutes, or until the meringue is set and the top has turned to a light brown color. Remove it from the oven and allow it to cool in the pan.

Assembling the Brazo de Mercedes:

When the meringue has cooled to room temperature, using a sieve, very lightly dust the top of the meringue with powdered sugar. Place a large piece of parchment paper, big enough to cover the meringue, on top over the meringue. Gently invert the meringue onto the parchment paper, and let it sit on a flat surface. Peel off the parchment paper on top the meringue was baked with.

Spoon the ube custard mixture evenly over the meringue, leaving about 1/4" without filling at the far 13" end. Starting on the closer 13" end (with filling), carefully roll the meringue along the short 13" side, into a log.

Transfer this onto your serving dish, and refrigerate for about 1 hour. Before serving, cut the 2 ends to create neat ends to the roll. Enjoy!