Preheat oven to 180°C (356°F) and line a baking sheet with baking paper.
In a medium bowl, whisk together flour, baking soda, and salt.
In a small bowl, mix buttermilk with vanilla extract.
In a large bowl, beat softened butter with sugar for 3 minutes until creamy. Add egg and mix well.
Alternate adding the buttermilk mixture and flour mixture to the butter mixture, beginning and ending with the flour mixture, until just combined.
Using a tablespoon, place 6 equal portions of dough on the prepared baking sheet, spacing them with room to spread. Bake for 15 to 17 minutes until golden brown on top. The centers should feel firm when pressed lightly, and do not let the bottoms brown too dark.