Combine 3 tablespoons very cold water, 1 teaspoon apple cider vinegar, and 1/2 cup ice in a liquid measuring cup or small bowl. Whisk to combine, and transfer to the refrigerator while you work with the other ingredients.
While the liquid is chilling, use a sharp knife to slice 1/2 cup very cold unsalted butter into 1-inch cubes. Transfer to the freezer to chill while you work with the other ingredients.
In the bowl of a food processor, combine 1 1/4 cups all-purpose flour, 1 1/2 teaspoons granulated sugar, and 1/2 teaspoon kosher salt. Pulse 2 to 3 times until the ingredients are combined. Remove the chilled butter from the freezer and add to the dry ingredients; continue pulsing in short 5 second intervals until the mixture resembles cornmeal with no butter pieces larger than the size of your thumb.
Once the mixture resembles cornmeal, remove the liquid mixture from the refrigerator and add 3 tablespoons to the dry ingredients. Pulse another few times and pick up a tablespoon of the dry ingredients with your hands and give it a squeeze. If the mixture holds together, dump it out into a medium bowl and use your hands to knead it together into a ball. If the mixture still feels dry and crumbly, add another tablespoon of water and test it again.
Wrap the dough ball up in plastic wrap and punch it down so it resembles a disc. Transfer to the refrigerator to chill for 1 hour, preferably overnight.