In a stand mixer fitted with a paddle, paddle together the flour, sugar, and salt for 10 to 15 seconds. Cut the butter into about 12 pieces and add it to the flour mixture. Paddle slowly until the flour is no longer bright white and the mixture holds together when you clump it, and there are still lumps of butter the size of pecans throughout…30-45 seconds.
Whisk together the egg yolk and milk in a small bowl and add them all at once to the flour-butter mixture. Paddle very briefly, just until it barely comes together, about 30 seconds it will look really shaggy and more like a mess than a dough.
Dump the dough out into a clean work surface and gather it together into a tight mound. Using the heel of your hand, smear the dough starting at the top of the mound and sliding your hand down the sides of the mound along the work surface, until most of the butter chunks are smeared into the dough and the whole thing comes together. (The technique is called fraisage, and makes for a very flaky pie dough.)
Wrap the dough tightly with plastic wrap and press down to make a disk about 1 inch thick. Refrigerate for at least 1 hour before using.
The dough can be stored in the refrigerator for up to 4 days or in the freezer for up to 4 weeks. Wrap in another layer of plastic if storing for more than 1 day