Sift the flour onto your work surface and shape it into a mound with a well in the center. Into the well, plop the salt, sugar, egg yolks or whole egg, and 2 tablespoons milk, cream, or water.
Using a spoon, stir the ingredients in the well until combined. Then gradually mix in the butter with the liquid ingredients in the well. Finally, using your hands, work the flour into the center of the well to combine it with the other ingredients. If necessary, add another tablespoon milk, cream, or water to create a smooth, soft dough. The dough must not be too firm. Do not overwork it, otherwise it'll be tough. When it’s ready, the dough will be barely moistened and come together into a ball.
Working the pie crust dough as little as possible, gently divide it into 2 equal portions and shape them into disks. Stash the dough in resealable plastic bags and refrigerate until chilled through. (Because of the copious amount of butter in the dough, it may be a little tricky to roll out. Having the dough be properly chilled through helps minimize stickiness.)
Roll out the pie crust dough. It helps to roll it out between sheets of parchment paper or to simply forget rolling and instead press it into two 9-inch tart pans. Proceed with your preferred tart recipe.