Ube Chiffon Cake Layer:

Preheat the oven to 350 F (175 C). Line a half sheet pan (13" x 18") with parchment paper. Do not grease the pan or the parchment paper.

In a large bowl, sift together the dry ingredients and combine well. Add in wet ingredients. Beat with an electric mixer or by hand just until smooth or well blended.

In a separate bowl, beat together 4 egg whites and 1.5 tsp cream of tartar on high speed until frothy. Gradually add in 2 tbsp sugar and beat until stiff peaks are formed. Gradually and gently fold in this meringue into cake mixture until well combined. Pour this into the prepared jelly roll pan, and smooth the top with the spatula.

Bake for about 20 minutes or until a toothpick inserted into the center of the cake comes out clean.

Place a rectangular piece of wax paper that's bigger than the cake on the surface, and invert the cake onto wax paper and slowly remove the baking pan so that parchment paper is on top. Then slowly peel off the parchment paper. Let it cool to room temperature.

Ube Custard Layer:

In a double boiler over low heat, whisk together 5 egg yolks, 1/4 can of condensed milk, 1/2 a cup of whole milk, 1/2 a cup of ube
halaya, 2 tsp of ube extract, and 2 tablespoons of butter. Cook this on low heat to prevent egg yolks from curdling, whisking regularly, for about 30 minutes or until the mixture thickens into a spreadable paste. Set this aside to cool to room temperature.

Frosting:

Combine cold cream cheese, sugar, and vanilla extract in a large mixing bowl. Fit the mixer with the whisk attachment and mix on medium speed until smooth. While the mixture is still whipping, slowly pour in very cold heavy cream. Continue whipping until the cream can hold stiff peaks. Put this frosting in the fridge till you're ready to assemble the cake.

Ube Mousse:

Sprinkle 1 tbsp. (or 1 packet, about 1/4 oz) of powdered gelatin
into 1/2 cup of cool water, making sure they are evenly distributed. Let it bloom for 5 to 10 minutes.

Meanwhile, warm 1/2 cup ube halaya in a metal bowl over a double boiler till it is warm. Melt in half a stick of butter, 1/8 teaspoon of salt, 1 teaspoon of ube extract, and 5 drops of purple food coloring, and mix until smooth.

Pour the swollen gelatin and water mixture into warm ube
mixture in gentle heat (double boiler). Mix until the gelatin is completely dissolved. Once dissolved, remove from the double boiler and let it cool. Be careful not to boil the gelatin, as this could prevent it from setting properly.

Meanwhile, in a metal or glass bowl, whip 2 cups of very cold heavy cream till it forms stiff peaks.

Clean and dry the beater attachments. Then in a separate smaller metal bowl, take the 5 egg whites remaining from the ube
custard yolks, and whip them (with clean, dry beaters) while slowly adding 2 tbsp of sugar. Stop when it makes soft peaks.

First fold in the whipped heavy cream, very gently - add 1/3 of the heavy cream at a time to temper the mixture. Then finally, even more gently, fold in the whipped egg whites - till the entire mixture is completely and thoroughly combined and uniform. Assemble cake immediately.

Assembling Cake:

Cut chiffon cake with a 9-inch metal cake ring. Put a metal cake ring in the middle of a cake stand. Put a piece of acetate sheet that's 4" high and 30" long inside the cake ring. Put chiffon cake at the bottom.

Then add the layer of ube custard. Then add the layer of ube mousse.

Then finally put the frosting in a piping bag and create little turrets of whipped cream frosting all over the top of the cake. Refrigerate overnight for the mousse to set. At least 8 hours, but 24 hours is best for the gelatin in mousse to set.

Slip off the metal cake ring, and peel off the acetate sheet to reveal the layers of cake. Serve while cold. Enjoy!