In a large bowl, whisk together the flour and either the sugar (for a sweet crust) or salt (for a savory one).
Add the cold butter cubes and toss to coat them in flour.
Using a pastry cutter or your fingertips, quickly cut the butter into the flour until the mixture resembles coarse crumbs with some pea-sized pieces of butter remaining.
Drizzle the oil over the mixture and toss to combine.
Sprinkle 3 tablespoons (45 ml / 1.5 fl oz) of ice water over the dough and gently mix with a fork until it starts to come together. If it's too dry, add the remaining tablespoon of water. The dough should be shaggy but hold together when squeezed.
Gently gather the dough into a ball and knead it on the counter just 3 or 4 times to bring it together.
Do not overwork it. Flatten the ball into a 1-inch thick disc.
Food Processor Method:** Combine flour, sugar or salt, and cold butter in the food processor bowl. Pulse 5-7 times until the mixture looks like coarse meal. With the machine running, stream in the oil, then the ice water. Stop the machine the moment the dough begins to form a ball.
Transfer to a counter and flatten into a disc.
On a lightly floured surface, immediately roll the dough disc into a 12-inch circle, about ⅛-inch thick. Rotate the dough often to prevent sticking and ensure an even circle.
Gently transfer the dough to a 9- or 10-inch pie plate or tart pan. A great trick is to loosely roll it around your rolling pin to lift and unroll it over the pan.
Press the dough into the bottom and up the sides of the pan. Trim any excess dough and flute the edges as desired. If using a tart pan, simply roll your rolling pin over the sharp edge to get a clean cut.
Chill the crust in the freezer for 15 minutes or in the refrigerator for at least 30 minutes. This step is essential to prevent shrinkage during baking.
To Blind Bake (Pre-Bake):** Preheat your oven to 400°F / 200°C. Prick the bottom of the chilled crust with a fork.
Line the crust with parchment paper or foil and fill with pie weights or dried beans.
Bake for 10-12 minutes. Carefully remove the paper/foil and weights, then bake for another 5-7 minutes, or until the bottom is lightly golden.
Let cool before filling.
Don't overmix the dough after adding water. Visible, pea-sized butter pieces are the secret to a tender, layered crust.
When rolling, rotate the dough a quarter turn after each pass with the rolling pin. This helps create an even circle and prevents it from sticking to your work surface.