Divide the butter into two parts, about two-thirds to one-third (5 tablespoons and 3 tablespoons). Cut the butter into 3/4 inch cubes. Wrap each portion of butter with plastic wrap. Refrigerate the larger amount and freeze the smaller for at least 30 minutes. Place the flour, salt, and optional baking powder in a reclosable gallon-size freezer bag and freeze for at least 30 minutes.

Place a medium mixing bowl in the freezer to chill.

Place the flour, salt, and optional baking powder in another medium bowl and whisk to combine them. Use a pastry cutter or rub the mixture between your fingers to blend the larger portion of the butter into the flour until it resembles coarse meal.

Spoon the mixture, together with the cold butter, into a reclosable gallon-size freezer bag. Expel any air from the bag and close it. Use a rolling pin to flatten the butter into flakes. Place the bag in the freezer for at least 10 minutes or until the butter is very firm.

Transfer the mixture to the chilled bowl, scraping the sides of the bag. Set the bag aside. Sprinkle the ice water and vinegar onto the mixture, tossing it lightly with a rubber spatula. Spoon the loose mixture back into the plastic bag.

Holding both ends of the bag opening with your fingers, knead the mixture by alternately pressing it, from the outside of the bag, with the knuckles and heels of your hands until the mixture holds together in one piece and feels slightly stretchy when pulled.

Wrap the dough with plastic wrap, flatten it into a disc and refrigerate for at least 45 minutes, preferably overnight.