Preheat the oven to 375 degrees F (190 degrees C).

Sift together flour, sugar, baking soda, and salt into a large bowl. Rub in butter until mixture appears sandy. Stir in buttermilk, a little at a time, until dough holds together.

Transfer dough to a lightly floured surface and roll out to a 1/8-inch thickness. Cut into 4-inch squares; cut each square diagonally into triangles, then prick with a fork. Place on ungreased cookie sheets.