In a medium saucepan, combine ½ cup of unsalted butter, ½ cup of whole milk, ½ cup of water, 1 tablespoon of granulated sugar, and a pinch of salt. Bring this mixture to a gentle boil over medium heat, stirring until the butter melts completely.

Once boiling, remove the saucepan from heat and add in 1 cup of all-purpose flour all at once. Stir vigorously until a smooth dough forms that pulls away from the sides of the pan, about 1-2 minutes.

Allow the dough to cool for about 5 minutes, then add 3 large eggs one at a time, mixing vigorously after each addition until the dough becomes glossy and smooth.

Preheat your oven to 400°F (200°C) while preparing a baking sheet lined with parchment paper. Portion the dough into 2-inch rounds on the tray, leaving space for expansion.

Place the baking sheet in the preheated oven and bake for 10 minutes. Reduce the temperature to 350°F (175°C) and continue baking for an additional 20 minutes.

Once golden, remove the puffs from the oven and let them cool on a wire rack for about 10-15 minutes.

In a medium saucepan, whisk together 1 cup of ube halaya, ½ cup of whole milk, 1 cup of heavy cream, ¼ cup of sugar, 2 tablespoons of cornstarch, and 2 egg yolks. Cook over medium heat, stirring until it thickens enough to coat the back of a spoon, about 5-7 minutes.

Remove from heat, stir in 1 teaspoon of vanilla extract, cover with plastic wrap, and chill in the refrigerator for at least 30 minutes.

Once the puffs are cool, cut a small hole in each and fill with the chilled ube custard using a piping bag.

Dust with powdered sugar if desired and serve cold or at room temperature.