Cream butter and sugar in a large bowl.
Add the eggs and vanilla and mix well.
Add 2 cups of the flour, the baking soda and salt; mix until just combined.
Add about half of the buttermilk and stir.
Add the remaining flour; mix; scrape down the sides of the bowl.
Finally, stir in the remaining buttermilk.
Cover the dough with plastic wrap and refrigerate for at least 1 hour and up to 24 hours. Do NOT skip the chill time!
Preheat oven to 350°F and line baking sheets with parchment paper or silicone baking mats.
Scoop the cookie dough onto the prepared cookie sheets and bake for 8-10 minutes, or until very a very light golden brown around the edges.
Remove from the oven; let set for 5 minutes then remove to a wire cooling rack.