Mix together vinegar and 8 tablespoons (1/2 cup) of milk. Set aside and keep cool.
In a medium bowl, stir together flour, salt and sugar.
Scatter butter chunks over the flour mixture and with either a fork or a pastry blender cut the butter into the flour, meaning incorporate the butter into the flour until the butter is about the size of small peas
Pour in the buttermilk and using a spatula or spoon, gently stir to bring the dough together, adding additional milk 1 tablespoon at a time until dough from loose clumps or curds. You may not need all the liquid.
Turn the dough out onto plastic wrap and form into a disc shape. At this point the dough can be refrigerated for later use (up to a couple days) or rolled out immediately. If you are saving for later, let dough sit at room temp for about an hour as a dough straight from the fridge will be difficult to roll.
This recipe makes enough for one double pie crust (top and bottom crust), or two single layer pies. Only roll out half the dough at a time.