Cream butter; gradually add 2 cups sugar, beating well.
Add eggs, one at a time, beating well after each addition.
Add buttermilk, and beat well.
Combine flour and soda; gradually stir into creamed mixture.
Stir in vanilla.
Chill dough several hours or overnight.
Roll dough to '1/4-inch thickness on a lightly floured surface; cut into rounds with a large biscuit cutter or a 3 1/2-inch cookie cutter.
Place rounds 1 inch apart on lightly greased cookie sheets; sprinkle with additional sugar.
Bake at 400Â° for 7 to 8 minutes or until edges are lightly browned.
Remove cookies to wire racks, and let cool completely.