In a saucepan, combine whole milk, heavy cream, egg yolks, ube extract, granulated sugar, cornstarch, and salt. Cook over medium heat until thickened, stirring constantly for about 10-12 minutes.

Remove the saucepan from heat and stir in the unsalted butter until fully melted and incorporated. Allow the cream to cool while occasionally stirring to prevent a skin from forming.

In a separate pot, combine all-purpose flour, water, whole milk, unsalted butter, granulated sugar, and salt. Cook over medium heat, stirring until the mixture forms a smooth ball, about 5-7 minutes.

Remove the dough from heat and let it cool slightly, around 5 minutes. Incorporate the eggs one at a time, mixing well until the dough is smooth and pipeable.

Preheat your oven to 375°F (190°C). Line a baking sheet with parchment paper. Pipe small rounds of dough onto the sheet, leaving space between each.

Bake the cream puffs for 25-30 minutes or until they are golden brown and feel hollow when tapped. Remove from the oven and let them cool completely on a wire rack.

Once cooled, gently fill each puff with the prepared ube pastry cream, using a piping bag or a small spoon.