Drizzle 1/2 cup of the ice-cold water (but not the cubes, if there are any left!) over the butter and flour mixture.
Using a rubber or silicon spatula, gather the dough together. You'll probably need an additional 1/4 cup of cold water to bring it together, but add it a tablespoon as a time. Once you have large clumps with the spatula, mix with your hands .
Gather the clumps together, kneading them gently.