In a heat safe mixing bowl, combine the ube powder and boiling water. Whisk the powder and cover with a lid. Leave to soak in the water for 20 minutes.
Whisk the ube mixture again to incorporate all the water and hydrated ube in the bowl. Add the contents into a saucepan over medium heat.
Bring to a simmer and continue to whisk for an additional 10 minutes or until the texture has the consistency of a thick apple sauce. Here's how it should look.
Remove the pan from the heat and add the evaporated milk, condensed milk, and vanilla extract.
Bring the pan back onto the heat over medium-high and bring to a boil. Lower the heat to medium-low and continue to stir to prevent the bottom from burning. Cook for another 10 minutes or until the ube halaya turns into a thick paste. Here's how the final texture should look.
Transfer the ube halaya into a jar and let rest until cool to serve or use as an ingredient.