Preheat oven to 325F. Line your baking sheet with parchment paper.
In a medium sized mixing bowl, beat butter, sugar, salt together until well incorporated and butter is light and fluffy.
Beat in egg, water, vanilla, ube extract. Then add flour and mix until mixed together. Dough will be stiff.
Refrigerate dough for 15 minutes. Then take 2 teaspoons of dough and roll into a ball. Repeat. Place the dough balls onto your baking sheets, leaving 2" space between them.
Place a small square of parchment paper on top of the ball and use a flat bottomed glass to squish the cookies to 3/16" thick.
Bake the cookies for 10 minutes. If more crispy cookies are wanted, you can bake up to 14 minutes. Cool them on a rack or on the pan.
Make the filling while the cookies cool down. Beat the sugar, butter, and vanilla extract together until mixture is light, fluffy, and color is white.
Add the cold water and beat until smooth and spreadable. Mixture will be stiff, but can be flattened between two cookies.
To fill the cookies, take a heaping teaspoon of filling and place into the middle of one cookie. Place another cookie on top and gently squeeze until filling is distributed evenly.
