This was from my great-grandmother and my grandmother made them all the time.
original recipe - makes about 2 doz., but I usually double it.
1/2 C butter
1 cup sugar
1 egg
1 tsp vanilla
1 tsp baking soda
1/2 cup buttermilk
2 cups flour
Cream butter and sugar. Mix in Egg and vanilla. I usually mix in the baking soda at this point. Then alternate the buttermilk and flour. I usually do 1/4 B-milk, mix thoroughly, then add 1/4 of the flour and mix. and so on three more times.
Drop by spoon onto cookie sheet, sprinkle with sugar and bake 8 minutes or so at 350 deg F.