Place 2/3 cup of milk into a pot. Reserve the remaining 1/3. In a bowl, whisk together the vanilla, yolks, and sugar. Whisk in the flour. In small amounts, add the reserved 1/3 cup of milk to assist with smoothing out the mixture. Set aside.
STEP 2
Bring the 2/3 cup of milk to a boil. Slowly pour the boiling milk into the egg mixture. Pour back into the pot and return to medium heat. Whisk continously until the first boiling bubbles appear.
STEP 3
Remove from the heat and strain through a sieve immediately. Stir in the ube paste. Spread out onto a pan in a thin lay and cover to cool rapidly.
STEP 4
While the cream is still cooling, take the day-old croissants and make a hole in the bottom by inserting a pairing knife and twisting. Once the ube pastry cream has cooled, place the mixture into a piping bag fitted with a round tip and pipe into the bottom of the croissant.
STEP 5
For the ube icing, place the icing sugar into a bowl. Add 2 tablespoons of water to the icing sugar and stir until smooth. If the constistency is too thick, add additional water, 1 tablespoon at a time, until desired constistency is reached. Add 2-3 drops of the ube extract, or until desired colour has been achieved.
