In a small bowl, stir together flour, baking soda, and baking powder. Set aside.
In a large bowl, cream together butter and sugar until smooth. Beat in the egg and vanilla. Gradually blend in dry ingredients. Add enough of the buttermilk to moisten the dough and make it soft, not wet.
Roll rounded teaspoons of dough into balls and place on a ungreased cookie sheet. With a brush or fingers, moisten the top of each cookie with the remaining buttermilk and slightly flatten the top of each cookie. Sprinkle with raw sugar or colored sprinkles.
Bake for 8 to 10 minutes or until slightly golden. Let stand for 2 minutes before removing to cool on a rack.