01 - In a mixing bowl, whisk together ube halaya, sweetened condensed milk, evaporated milk, heavy cream, and ube extract until a smooth, uniform consistency is achieved.
02 - In a small saucepan, mix whole milk, heavy cream, and granulated sugar. Sprinkle gelatin or agar-agar over the mixture and allow it to bloom for 5 minutes. Gently heat over low flame, stirring until the thickener dissolves completely without boiling. Add vanilla extract, then remove from heat and let cool slightly.
03 - Arrange a slice of sponge cake at the base of each serving glass. Spoon a generous layer of the ube mixture over the cake. Pour a layer of milk jelly over the ube layer. Repeat layering if space allows, finishing with milk jelly on top.
04 - Refrigerate filled glasses for at least 2 hours until the jelly layer is completely set.
05 - Before serving, top each glass of trifle with whipped cream and garnish with fresh ube cubes or purple sprinkles as desired.