In a saucepan, combine whole milk, heavy cream, egg yolks, ube extract, granulated sugar, cornstarch, and salt. Cook over medium heat, stirring continuously until it thickens and coats the back of a spoon.

Once thickened, remove from heat and stir in the unsalted butter until completely melted. Set aside to cool.

In another pot, combine all-purpose flour, water, whole milk, granulated sugar, and salt. Cook over medium heat, stirring until the mixture forms a smooth ball that pulls away from the sides of the pot.

Allow the mixture to cool slightly. Then, incorporating eggs one at a time, stir vigorously until the dough is smooth and pipeable.

Preheat your oven to 375°F (190°C). Line a baking sheet with parchment paper. Using a pastry bag, pipe small rounds of dough onto the sheet.

Bake in the preheated oven for about 25-30 minutes until the puffs are golden and sound hollow when tapped. Let them cool completely on a wire rack.

Once cooled, gently cut the tops off the puffs and fill them with the prepared pastry cream. Replace the tops and dust with powdered sugar if desired.