The addition of vinegar helps to "tenderize" the dough. You can use any kind of vinegar if you don't have Champagne vinegar. This recipe makes about 3 pounds of dough, which is enough for 24 empanadas.
5 cups all-purpose flour
4 sticks (2 cups) cold unsalted butter, cut into 1/2-inch cubes
1 large egg
1 tbsp. Champagne vinegar
About 3/4 cup ice water
1. Sift flour with salt into a large bowl and blend in butter with your fingertips or a pastry blender until most of mixture resembles coarse meal with small (roughly pea-size) butter lumps.
2. Beat egg with vinegar in a 1-cup measure using a fork, then add enough ice water to measure 1 cup total. Add to flour mixture, stirring with fork until incorporated.
3. Turn out mixture onto a lightly floured surface and knead gently with heel of your hand just enough to bring dough together. Roll out or pat into a 15 x 9-inch rectangle. Arrange dough with short side nearest you, then fold into thirds like a letter to form a roughly 5 x 9-inch rectangle. Chill dough, wrapped in plastic wrap, at least 1 hour and up to 6 (do not chill longer or dough will discolor).