Start by gathering all your ingredients and tools. Preheat your oven to 350°F (175°C), and line your baking sheets with parchment paper.
In a medium bowl, whisk together the all-purpose flour, baking soda, and baking powder.
In a large mixing bowl, combine the softened butter and white sugar. Use an electric mixer on medium speed to cream them together until light and fluffy, about 3-5 minutes.
Add the egg and vanilla extract to the creamed mixture. Mix until fully incorporated.
Gradually add the dry ingredient mixture to the wet ingredients. Mix on low speed until just combined.
Stir in 3 to 4 tablespoons of buttermilk.
Using a cookie scoop, drop rounded balls of dough onto the prepared baking sheets, spacing them about 2 inches apart. Sprinkle with colored sugar or sprinkles if desired.
Bake for 8-10 minutes, or until the edges are lightly golden. The centers may look slightly underbaked.
Allow the cookies to cool on the baking sheets for about 5 minutes before transferring them to a wire rack to cool completely.
