Preheat the oven to 375°F.
Line two baking sheets with parchment paper.
Set the prepared baking sheets aside.
In a medium mixing bowl, combine the all-purpose flour, baking soda, and salt.
Stir until the dry ingredients are evenly distributed.
In a large mixing bowl, beat the softened unsalted butter and granulated sugar with an electric mixer.
Continue mixing for 5 to 7 minutes, or until the mixture is light and fluffy.
Add the room-temperature egg and vanilla bean paste or pure vanilla extract.
Mix until fully incorporated.
Add the dry ingredients and buttermilk alternately to the butter mixture.
Mix well after each addition.
Continue until a soft, thick batter forms.
Scoop the cookie batter onto the prepared baking sheets.
Leave approximately 2 inches of space between each portion of batter.
Bake for 10 to 11 minutes, or until the cookies are set.
Remove the baking sheets from the oven.
Allow the cookies to cool on the baking sheets for approximately 5 minutes.
Transfer the cookies to a wire rack.
Allow the cookies to cool completely before filling.